ATM Alterations Research Articles

TMPRSS2:ERG Gene Fusion Might Predict Resistance to PARP Inhibitors in Metastatic Castration-resistant Prostate Cancer.

The emergence of novel DNA damage repair (DDR) pathways in molecular-target therapy drugs (MTTD) has shown promising outcomes in treating patients with metastatic castration-resistant prostate cancer (mCRPC). About 25% of mCRPC patients have actionable deleterious aberrations in DDR genes, primarily in the homologous recombination (HR) pathway. However, the response rate in patients with BRCA1/2 or mutations in HRR-related genes is only 45%-55%, when exposed to poly ADP ribose polymerase (PARP) inhibitor-based therapy (PARPi). A frequent characteristic feature of prostate cancer (PC) is the occurrence of genomic rearrangement that affects the transmembrane protease serine 2 (TMPRSS2) and E26 transformation-specific (ETS)- transcription factor-related gene (ERG). In this study, a total of 114 patients with mCRPC had their RNA and DNA sequenced using next-generation sequencing. Based on their genetic profile of deleterious gene alterations of BRCA1/2 or ATM, six patients were selected for PARPi. Patients with TMPRSS2:ERG gene fusion and homozygous alteration in ATM or BRCA2 (n=2) or heterozygous alterations (BRCA1 or BRCA2) and lack of TMPRSS2:ERG gene fusion (n=2) did not show clinical benefit from PARPi (treatment duration <16 weeks). In contrast, patients (n=2) without TMPRSS2:ERG gene fusion and homozygous deleterious alterations in ATM or BRCA2 all had clinical benefit from PARPi (treatment duration ≥16 weeks). The TMPRSS2:ERG transcript product might be used as a PARPi resistance biomarker.

90P Clonal haematopoiesis of indeterminate potential (CHIP) might mislead interpretation of ATM and CHEK2 alterations detected on liquid biopsies

90P Clonal haematopoiesis of indeterminate potential (CHIP) might mislead interpretation of ATM and CHEK2 alterations detected on liquid biopsies

Abiraterone, Olaparib, or Abiraterone + Olaparib in First-Line Metastatic Castration-Resistant Prostate Cancer with DNA Repair Defects (BRCAAway).

Deleterious germline/somatic homologous recombination repair mutations (HRRm) are present in ∼25% of patients with metastatic castration-resistant prostate cancer (mCRPC). Preclinically, poly(ADP-ribose) polymerase (PARP) inhibition demonstrated synergism with androgen receptor pathway (ARP)-targeted therapy. This trial evaluated the efficacy of ARP inhibitor versus PARP inhibitor versus their combination as first-line therapy in patients with mCRPC with HRRms. BRCAAway is a biomarker preselected, randomized, phase 2 trial. Patients with BRCA1/2 and/or ATM alterations were randomized 1:1:1 to Arm1: abiraterone (1,000 mg)/prednisone (5 mg BID) (Abi/pred), Arm2: olaparib (300 mg BID) (Ola), or Arm3: abiraterone/prednisone + olaparib (Abi/pred + Ola). Single-agent arms could cross over at progression. Exploratory Arm4 patients with other HRRms received olaparib alone. The primary endpoint was progression-free survival (PFS), and secondary endpoints were objective response, PSA response, and safety. Sixty-one of 165 eligible patients had BRCA1/2 or ATM mutations: median age: 67 (IQR, 62-73) years. Mutations: BRCA1 n = 3, BRCA2 n = 46, ATM n = 11, and multiple n = 1; 33 germline and 28 somatic mutations. Median PFS [95% confidence interval (CI)]: Abi/pred, 8.6 months (m; 2.9, 17), Ola, 14 m (8.4, 20), and Abi/pred + Ola, 39 m [22, not reached (NR)]. There were no G4/5 adverse events; 8/19 patients on Abi/pred treatment crossed over to Ola, and 8/21 vice versa. Median PFS (95% CI) from crossover: Ola-after-Abi/pred, 8.3 m (5.5, 15) and Abi/pred-after-Ola, 7.2 m (2.8, NR). Median PFS (95% CI) from randomization: Ola-after-Abi/pred, 16 m (7.8, 25) and Abi/pred-after-Ola, 16 m (11, NR). Seventeen of 165 patients with other HRRms received olaparib: median PFS (95% CI): 5.5 m (2, 11). In patients with mCRPC with BRCA1/2 or ATM HRRm, Abi/pred + Ola was well tolerated and demonstrated longer PFS versus either agent alone or sequentially.

Genotype-Directed Synthetic Cytotoxicity of ATR Inhibition with Radiotherapy.

The importance of the DNA damage response in mediating effects of radiotherapy (RT) has galvanized efforts to target this pathway with radiosensitizers. Yet early clinical trials of this approach have failed to yield a benefit in unselected populations. We hypothesized that ataxia-telangiectasia mutated (Atm)-null tumors would demonstrate genotype-specific synergy between RT and an inhibitor of the DNA damage response protein ataxia-telangiectasia and Rad3-related (ATR) kinase. We investigated the synergistic potential of the ATR inhibitor (ATRi) RP-3500 and RT in two Atm-null and isogenic murine models, both in vitro and in vivo. Staining of γ-H2AX foci, characterization of the immune response via flow cytometry, and tumor rechallenge experiments were performed to elucidate the mechanism of interaction. To examine genotype specificity, we tested the interaction of ATRi and RT in a Brca1-null model. Finally, patients with advanced cancer with ATM alterations were enrolled in a phase I/II clinical trial to validate preclinical findings. Synergy between RP-3500 and RT was confirmed in Atm-null lines in vitro, characterized by an accumulation of DNA double-strand breaks. In vivo, Atm-null tumor models had higher rates of durable control with RT and ATRi than controls. In contrast, there was no synergy in tumors lacking Brca1. Analysis of the immunologic response indicated that efficacy is largely mediated by cell-intrinsic mechanisms. Lastly, early results from our clinical trial showed complete responses in patients. Genotype-directed radiosensitization with ATRi and RT can unleash significant therapeutic benefit and could represent a novel approach to develop more effective combinatorial synthetic cytotoxic RT-based treatments.

Abstract CT222: Efficacy and safety of ceralasertib in the PLANETTE study in patients (pts) with ATM-altered advanced solid tumors (ASTs) or metastatic castration-resistant prostate cancer (mCRPC)

Abstract Background: Ceralasertib, a potent, selective ATR inhibitor, is synthetically lethal in ATM-deficient preclinical models. This Phase 2a study (NCT04564027) assessed ceralasertib monotherapy in previously treated pts with ATM-altered tumors. Methods: Adult pts had ASTs excluding NSCLC (Cohort [Co] A; data cutoff [DCO] Dec 21 2022) or mCRPC (Co B; DCO Apr 28 2023) and germline/somatic ATM pathogenic/likely pathogenic variants (PVs) by local assessment. ATM alterations were centrally confirmed by FMI F1CDx in tumor and/or FMI F1 liquid CDx in circulating tumor DNA, and/or by ATM protein deficiency by immunohistochemistry (cutoff ≤5%). Primary endpoints were objective response rate (ORR) in Co A and composite response rate (CRR) in Co B. Safety was a secondary endpoint. Results: The initial starting dose of 240 mg BID PO ceralasertib on Days 1-14 of a 28-day cycle was reduced to 160 mg BID due to hematologic toxicity. Results are reported for 30 pts in Co A and 15 pts in Co B with a starting dose of 160 mg BID. In Co A, the 28 pts with centrally confirmed ATM alterations (93.3% [28/30] with ATM PV and 36.7% [11/30] ATM-deficient) had an ORR of 7.1% (80% CI: 1.9, 17.9): 1 complete response in breast cancer (ongoing at 12 mos) and 1 partial response in endometrial cancer (ongoing at 9 mos), both ATM-deficient. In Co B, the 13 pts with centrally confirmed ATM alterations (73.3% [11/15] with ATM PV and 46.7% [7/15] ATM-deficient) had a CRR of 7.7% (80% CI: 0.8, 26.8): 1 pt with conversion of circulating tumor cell count from unfavorable to favorable (ongoing at 3 mos) with unknown ATM expression. The safety profile was manageable (Table). Steady-state ceralasertib plasma concentrations exceeded the IC90 for ~23 hrs/day. Conclusion: Responses to ceralasertib monotherapy were limited in ATM-altered tumors, despite reaching target plasma levels. Alternative pt selection and combination treatment strategies are being explored. TABLE 1: NAND Efficacy, safety of ceralasertib 160 mg BID on D1-14 of D28 cycle in pts with ATM-altered ASTs/mCRPC Cohort A: ASTs Cohort B: mCRPC Efficacy Response rate in pts with centrally confirmed ATM alterations, % (80% CI)* N=28 7.1 (1.9, 17.9)† N=13 7.7 (0.8, 26.8)‡ Response rate in pts with centrally confirmed ATM PVs, % (80% CI) N=28 7.1 (1.9, 17.9) N=11 9.1 (1.0, 31.0) Response rate in pts with centrally confirmed ATM-deficiency, % (80% CI) N=11 18.2 (4.9, 41.5) N=7 0.0 (0.0, 28.0) Safety, n (%) N=30 N=15 TEAEs 30 (100) 15 (100) Grade ≥3 TEAEs 15 (50.0) 8 (53.3) TRAEs 21 (70.0) 13 (86.7) Grade ≥3 TRAEs 6 (20.0) 5 (33.3) Serious TEAEs 4 (13.3) 4 (26.7) Serious TRAEs 2 (6.7) 1 (6.7) TEAEs leading to discontinuation 1 (3.3)§ 0 TEAEs leading to death 0 0 TEAEs (any grade) occurring in ≥20% of pts in either cohort, n (%) N=30 N=15 Nausea 13 (43.3) 8 (53.3) Abdominal pain 9 (30.0) 1 (6.7) Anemia 8 (26.7) 7 (46.7) Fatigue 8 (26.7) 5 (33.3) Asthenia 8 (26.7) 2 (13.3) Decreased appetite 7 (23.3) 3 (20.0) *Centrally confirmed ATM-altered patients were patients with either ATM PV confirmed by FMI F1CDx in tumor and/or by FMI F1 liquid CDx in circulating tumor DNA and/or ATM protein-deficient by immunohistochemistry assay at Ventana with cut-off ≤5%. Thus, ATM PV patients could also have ATM protein-deficiency. †Objective response by RECIST v1.1, in centrally confirmed ATM-altered patients. ‡Composite response: by RECIST v1.1 for soft tissue and visceral lesions and PCWG3 criteria for bone lesions; confirmed conversion of circulating tumor cell count from ≥5/7.5 mL blood to &amp;lt;5/7.5 mL; or confirmed prostate-specific antigen decline of &amp;gt;50%, in centrally confirmed ATM-altered patients. §Discontinuation due to decreased appetite classified as a serious adverse event. ASTs, advanced solid tumors; CI, confidence interval; mCRPC, metastatic castration-resistant prostate cancer; PV, pathogenic variant; pts, patients; TEAE, treatment-emergent adverse event; TRAE, treatment-related adverse event Citation Format: Rahul Aggarwal, Antoine Italiano, Susan Domchek, Oscar Goodman, Sophie Postel-Vinay, Jesus Garcia-Donas, Tanya Dorff, Zachery Reichert, Philippe Cassier, Neal Shore, Catherine Marshall, Graeme Parr, Itziar Irurzun-Arana, Neel Shah, Natalia Lukashchuk, Olga Murina, Daniel Slade, Bienvenu Loembé, Emma Dean, Elhan Sanai, Wassim Abida. Efficacy and safety of ceralasertib in the PLANETTE study in patients (pts) with ATM-altered advanced solid tumors (ASTs) or metastatic castration-resistant prostate cancer (mCRPC) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr CT222.

Abstract LB215: Polymerase θ (POLθ) inhibitors (novobiocin, ART-558, RP6685) were tested with 22 approved and investigational agents in multi-cell type spheroids of genetically selected patient-derived human tumor cell lines

Abstract The potential of novobiocin to augment cancer chemotherapy was explored in the late 1980s and early 1990s in tumor cells and tumor-bearing mice and in Phase 1 clinical trials with cyclophosphamide or cisplatin. The molecular target of novobiocin was identified to be DNA POLθ which has a role in repair of DNA double strand breaks (DSB) during mitosis. Genetic alterations which may increase or decrease POLθ inhibitor effects have been elucidated. Thirty patient-derived tumor cell lines with known BRCA, ATM, ATR, POLQ, XRCC1, PALB2, PARP1, and LIG3 alterations were screened in a complex spheroid assay (tumor cells, endothelial cells, mesenchymal stem cells) with a POLθ inhibitor (novobiocin, ART-558, or RP6685), alone or in simultaneous combination with a FDA approved or investigational anticancer small molecule, using a 7-day exposure and a CellTiter-Glo 3D luminescence endpoint. As single agents, the POLθ inhibitors had little or no cytotoxicity. Potentiation of the topoisomerase II inhibitors doxorubicin (DOX) and etoposide by the POLθ inhibitors ART-558 or RP6685 was observed in spheroids grown from the serous endometrial adenocarcinoma 922993-354-T-J3, which has ATM and BRCA2 variants. The 379773-124-R-J2 endometrioid endometrial adenocarcinoma which harbors mutant POLθ demonstrated antagonism with ART-558 in combination with PARP inhibitors and less than additive to additive cytotoxicity in combination with DOX. Activity of the Chk1/2 inhibitor prexasertib was potentiated by either ART-558 or RP6685 in the 922993-354-T-J3 complex spheroids. The combination of POLθ inhibitor ART-558 and the Chk1/2 inhibitor prexasertib produced up to 1 log increase in cytotoxicity in the 922993-354-T-J3 complex spheroids. KRAS G12D inhibitor MRTX-133 cytotoxicity against 186277-243-T-J2 colon adenocarcinoma with the KRAS G12D variant was potentiated by either ART-558 or RP6685. Potential combinations to advance into in vivo studies will be presented. This project was funded in part with federal funds from the NCI, NIH, under contract no. HHSN261201500003I. Citation Format: Beverly A. Teicher, Thomas S. Dexheimer, Thomas Silvers, Nathan P. Coussens, J Paul Eder, James H. Doroshow. Polymerase θ (POLθ) inhibitors (novobiocin, ART-558, RP6685) were tested with 22 approved and investigational agents in multi-cell type spheroids of genetically selected patient-derived human tumor cell lines [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB215.

Abstract A012: Genomic landscape of somatic alterations identified in endometrial cancer using liquid biopsy

Abstract Background: With advances in understanding the biology of endometrial cancer, molecular sub-groups have been defined to assess prognosis and guide treatment decisions. This classification is based on surrogate markers in archival paraffin-embedded tissues. The landscape of somatic alterations as detected by liquid biopsy has not been well described in advanced endometrial cancer. Methods: A retrospective analysis was performed using de-identified genomic data collected from patients with advanced endometrial cancer who underwent liquid biopsy testing with a 74-83 gene panel as part of clinical care (Guardant360, Guardant Health, Inc.). Results: 1,988 females with a median age of 68 [range 23-95] years were included in the analysis. 45% of patients were tested at diagnosis of advanced disease; 43% were tested at time of disease progression. 91.6% of patients had ≥1 somatic alteration detected and 12% of patients were MSI-High. The most frequently altered genes included TP53 (65%), PIK3CA (31%), PTEN (27%), ARID1A (24%), like prior reports of genomic alterations detected in tissue samples. CCNE1 amplifications were enriched in 11% of samples with TP53 alterations (p&amp;lt;0.0001; q&amp;lt;0.0001) and EGFR amplifications were enriched in samples without TP53 alterations (p&amp;lt;0.0001; q&amp;lt;0.0001). MSI-H samples were enriched for alterations in ARID1A, PTEN, PIK3CA, ATM, MSH6 and others, while samples without MSI were enriched for alterations in TP53 and CCNE1 (p&amp;lt;0.0001; q&amp;lt;0.0001). Oncogenic fusions were rare in this cohort (0.2%) and included FGFR1 and FGFR3 rearrangements. Activating, druggable alterations were identified in PIK3CA, KRAS, ERBB2, and BRCA1/2. Putative pathogenic germline alterations were detected in 61 (3%) patients and included ATM (18%), BRCA1 (33%), BRCA2 (21%), and lower frequencies of CHEK2, FANCA, MLH1, MSH2, MSH6, and PALB2. Conclusions: While descriptive in nature, this analysis is the largest cohort of advanced endometrial cancer analyzed using a clinically available liquid biopsy assay and demonstrates the feasibility of somatic alteration detection. This report paves the way for using liquid biopsy as a potential tool for guiding targeted chemotherapeutic strategies. Citation Format: Leylah Drusbosky, Ginger Haynes, Brooke Grant, Pamela Sobernis, Stephanie Lheureux. Genomic landscape of somatic alterations identified in endometrial cancer using liquid biopsy [abstract]. In: Proceedings of the AACR Special Conference on Endometrial Cancer: Transforming Care through Science; 2023 Nov 16-18; Boston, Massachusetts. Philadelphia (PA): AACR; Clin Cancer Res 2024;30(5_Suppl):Abstract nr A012.

Genomic predictors of response and resistance to 177-Lu-PSMA-617 using circulating tumor DNA.

220 Background: There is a critical need to identify biomarkers of response and resistance to 177Lu-PSMA-617. Post-hoc analyses of VISION have explored the prognostic and predictive value of select clinical parameters. However, we are still in the early stages of deciphering which molecular changes are associated with favorable or adverse treatment outcomes. Methods: We conducted a retrospective analysis of patients with metastatic castration-resistant prostate cancer (mCRPC), who received 177Lu-PSMA-617 at Mayo Clinic in Rochester, Minnesota, in the interval of March 2022 to March 2023. We included patients who provided research authorization, had a baseline PSA of at least 2 ng/mL, received at least 2 cycles of treatment, and had circulating tumor DNA (ctDNA) genomic profiling performed by Guardant (83 gene panel) within 60 days of treatment initiation. Clinical, laboratory, genomic, and radiomic parameters were abstracted by trained research personnel. Two independent analyses of “response” and “resistance” were performed. Response to treatment was defined as 50% or greater decrease in PSA from baseline (PSA50 response: dichotomized yes versus no), and resistance was defined as non-decreasing or rising PSA during treatment (PSA non-response: dichotomized yes versus no). Associations between gene alterations and response and resistance were evaluated via Fisher’s exact tests. Results: Between March 2022 and March 2023, 273 patients received cycle 1 of 177Lu-PSMA-617. A total of 108 patients met the inclusion criteria. The median number of cycles at data cutoff was 6 (IQR: 4,6) with 57 (53%) patients receiving all 6 planned cycles. The median PSA at baseline was 16.65 ng/ml (IQR: 5.20, 66.12). A total of 65 patients (60%) experienced a PSA50 response. No molecular alterations were associated with a higher rate of PSA50 response; however, alterations in ARID1A, AR, and CHEK2 were associated with lack of PSA50 response (Fisher’s exact p &lt; 0.05). Of the 108 evaluable patients, 20 (19%) met criteria for PSA non-response. Alterations in AR, ARID1A, MYC, TP53, CHEK2, ATM, EGFR, and NOTCH1 were significantly associated with PSA non-response (Fisher’s exact p &lt; 0.05); in each case, the presence of the alteration was positively associated with resistance (i.e., more instance of PSA non-response). No biomarkers were found to be inversely associated with PSA non-response. Conclusions: ctDNA assessed by commercially available, targeted sequencing panels prior to treatment may be useful in identifying the patients least likely to benefit from 177Lu-PSMA-617. Further work is ongoing to integrate ctDNA findings with clinical parameters in the hopes of understanding the factors mediating response and resistance to therapy.

Abstract B001: Identification of monoallelic ATM loss-of-function and homologous recombination deficiency (HRD) in high-grade ovarian tumor with prolonged response to camonsertib and low-dose gemcitabine combination therapy

Abstract Intra-tumor heterogeneity and the prevalent loss-of-function mutations within DNA damage repair (DDR) genes constitute salient hallmarks of high-grade ovarian malignancies. However, the etiological drivers beyond BRCA1/2 mutations, as well as the chronology of tumor evolutionary processes, remain enigmatic. Here, we present the case of a 60-year-old female with high-grade serous ovarian cancer, initially treated with primary debulking surgery followed by 6 cycles of adjuvant intraperitoneal cisplatin and paclitaxel. After a 16-month platinum-free interval, the patient (pt) developed recurrent disease and subsequently received 5 weeks of neoadjuvant olaparib followed by secondary debulking surgery and adjuvant carboplatin as part of a clinical trial (NCT02489006). The pt became platinum refractory after 4 cycles of carboplatin, then received weekly paclitaxel and biweekly bevacizumab with stable disease as best response and eventual progression after 17 cycles. Molecular profiling of the metastatic biopsies at the time of initial recurrence identified a pathogenic ATM (c.4910-1G&amp;gt;A) alteration for which the pt was then enrolled onto the Phase Ib TRESR trial (NCT04497116). The trial enrolled pts ≥18 years, ECOG PS 0-1, with advanced solid tumors with deleterious DDR alterations. The pt received a starting dose of 1000mg/m2 gemcitabine (gem) with 80mg of the ATR inhibitor camonsertib (cam; 3 days [d] on/4d off) on a 21d cycle (2 weeks [w] on/2w off). The pt had a partial RECIST 1.1 response at 4 months (mo) and remains on treatment after 18mo. Due to toxicities (primarily neutropenia) the pt had a series of dose reductions to 200mg/m2 gem with 50mg cam (2d on/5d off) on a 28d cycle (1w on/1w off). Circulating tumor fraction (TF), measured by methylation-based profiling, remained at or below the limit of quantitation of the assay through 11mo (0.01% TF, testing of later timepoints ongoing). At 13mo, the target lesions began increasing in size (-50% to -43%) prompting a dose increase of cam to 80mg (same gem dose), after which the target lesions decreased to nadir (-52%) at 76w with concomitant CA-125 decrease. Retrospective whole-genome sequencing (WGS) of the secondary debulking surgery specimen as well as targeted sequencing (SyNthetic lethal Interactions for Precision Diagnostics [SNiPDx]) and immunohistochemistry of the metastatic biopsy revealed ATM protein loss only in a portion of the tumor and a monoallelic ATM mutation. Genomic signature analysis of WGS indicated presence of single-base substitution signatures 3+8 (HRD-related) and HRD positivity (BRCA1-type; CHORD algorithm). In contrast, while HRD+ was also detected in the primary tumor sample, the ATM alteration was absent and ATM protein expression was uniform, suggesting that ATM loss was a late event in tumor evolution. This case highlights the complexity of intra-tumor heterogeneity and clonal evolution in ovarian tumors and importance of “functional” HRD as no apparent mutational driver was identified. Citation Format: Stephanie Lheureux, Joseph D. Schonhoft, Ian M. Silverman, Julia Yang, Adrienne Johnson, Brooke Grant, Alexander Fortuna, Trevor J. Pugh, Parham Nejad, Bernard Lam, Sahaj Arora, Ashley Adile, Stephenie D. Prokopec, Jeffrey Bruce, Danielle Ulanet, Maria Koehler, Ezra Rosen, Victoria Rimkunas. Identification of monoallelic ATM loss-of-function and homologous recombination deficiency (HRD) in high-grade ovarian tumor with prolonged response to camonsertib and low-dose gemcitabine combination therapy [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: DNA Damage Repair: From Basic Science to Future Clinical Application; 2024 Jan 9-11; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2024;84(1 Suppl):Abstract nr B001.

Inhibition of ATM with KU-55933 Sensitizes Endometrial Cancer Cell Lines to Olaparib.

Endometrial cancer (EC) is one of the most prevalent gynecologic cancers, which poses a serious threat to women's health worldwide. Olaparib, the first FDA-approved PARP inhibitor for the treatment of BRCA-mutated breast, ovarian and pancreatic cancers, triggers apoptosis of cancer cells through synthetic lethality by inhibiting PARP1/2 enzymatic activity and BRCA1/2-dependent homologous recombination (HR) repair deficiency. However, the synergistic lethal effects between Olaparib and inhibitors of other DNA damage response proteins, such as ATM, PTEN and RAD51, are still unknown. Exploring the synergistic lethal effect between Olaparib and KU-55933 on EC. The GEPIA database was used to test EC patient survival rate. CCK8 was used for cell viability assays. Western blot was used for examining gene levels. The wound healing assay was used to detect cell migration ability. Flow cytometry was used for detecting the apoptosis rate. All experimental conditions were repeated independently in triplicate and analyzed in three separate experiments. In this study, we discovered that the frequency of ATM alterations in endometrial cancer reaches nearly 20% and that there is a positive correlation between ATM alterations and prognosis. Furthermore, we discovered that endometrial cells with low expression levels of ATM are sensitive to Olaparib. Treatment with KU-55933, a specific inhibitor of ATM, significantly enhanced the sensitivity of endometrial cancer cells to Olaparib, as evidenced by colony formation, cell migration and apoptosis assay. Further analysis revealed that KU-55933 potentiates Olaparib-induced cell apoptosis by inhibiting ATM phosphorylation. Our study demonstrates that inhibiting ATM could enhance the sensitivity of endometrial cancer to Olaparib, thereby providing a potential alternative treatment for the clinical treatment of endometrial cancer.

Abstract A123: Circulating tumor DNA (ctDNA) genomic and epigenomic profiling (GuardantINFINITY) for diagnosis of DNA damage repair (DDR) loss of function (LOF) and response monitoring in the TRESR and ATTACC trials

Abstract Background First-generation panel-based ctDNA sequencing is widely used to identify actionable genomic alterations, but limited coverage and sensitivity hinder broader clinical utility, especially in cancers driven by DDR LOF. Further, tissue-free, variant-based approaches for response monitoring have several challenges, including the limited number and low variant allele frequencies (VAF) of monitorable variants and contamination from non-tumor-derived sources (eg, clonal hematopoiesis [CH]). Newer panels may address these challenges with broader coverage, optimized bioinformatics, and the integration of epigenetic analysis for molecular response (MR). Methods Blood samples were collected from 2 phase 1 studies (TRESR; NCT04497116 and ATTACC; NCT04972110) of the ataxia telangiectasia and Rad3-related (ATR) inhibitor camonsertib in combination with gemcitabine or PARPi (talazoparib, niraparib, or olaparib). Cell-free DNA and PBMCs were sequenced using the combined genomic (&amp;gt;800 genes) and methylation (15Mb) GuardantINFINITY platform. Results The study included 117 patients (pts) with ovarian (n=29), breast (n=18), pancreatic (n=18), prostate (n=16) and other (n=36) cancers, enrolled with pathogenic alterations in BRCA2 (n=41), ATM (n=32), BRCA1 (n=23), PALB2 (n=8) and other genes (n=13). Enrollment alterations identified by local NGS were confirmed in 83% (94/114) of pts excluding 3 enrolled by protein loss. 50% (5/10) of complex alterations (large deletions or rearrangements) with sufficient circulating tumor fraction (cTF) were confirmed. Among pts with breast, ovarian, prostate, or pancreatic cancers previously treated with PARPi and/or platinum and harboring BRCA1/2 or PALB2 alterations, reversions were detected in 31% (17/54), with 6 pts reverted by 1 or more large intragenic deletions. A CRC pt with a clonal biallelic sATM alteration had 2 missense reversions in cis, an event not previously reported to occur in ATM. In pts with matched PBMCs, confirmed CH alterations were detected in 79% (44/56), including 59% (33/56) with at least 1 CH variant over 1% VAF. 106 pts had evaluable paired samples at baseline and on-treatment (taken between 2-12 weeks on-treatment [median, 3 weeks]). Using mVAF of the Guardant360 74-gene subset or methylation-based cTF, 72% or 86% were monitorable, respectively. In the subset of evaluable pts with matched PBMC sequencing (n=54), after PBMC-informed CH filtering, monitorability was reduced from 69% to 61% between G360 mVAF and G360 mVAF-CH, respectively. PBMC-informed CH filtering improved the correlation between variant-based and methylation-based monitoring (G360 mVAF, R=0.89, p=1.1e-11 vs G360 mVAF-CH, R=0.95, p=3e-15; Pearson correlation). Correlation of ctDNA monitoring metrics with clinical outcomes is ongoing. Conclusions Broad panel coverage enabled accurate diagnosis of complex DDR LOF and detection of reversion alterations. Methylation-based cTF allows monitoring of most pts in this cohort and consistent with previous observations may avoid signal contamination from CH for robust MR analysis. Citation Format: Ezra Rosen, Joseph D Schonhoft, Ian M Silverman, Arielle Yablonovitch, Sunantha Sethuraman, Parham Nejad, Danielle Ulanet, Julia Yang, Insil Kim, Kezhen Fei, Yi Xu, Errin Lagow, Shile Zhang, Mingyang Cai, Maria Koehler, Benedito A Carneiro, Stephanie Lheureux, Michael Cecchini, Benjamin Herzberg, Jorge S Reis-Filho, Victoria Rimkunas, Timothy A Yap. Circulating tumor DNA (ctDNA) genomic and epigenomic profiling (GuardantINFINITY) for diagnosis of DNA damage repair (DDR) loss of function (LOF) and response monitoring in the TRESR and ATTACC trials [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr A123.

Prospective, Cell-Free Circulating Tumor DNA (ctDNA) Profiling in Locally Advanced Lung Cancer Treated with Chemoradiation

Liquid biopsy for cell-free circulating tumor DNA (ctDNA) allows for non-invasive, comprehensive genomic profiling. We explored the utility prospective liquid biopsy for (ctDNA) in among non-small cell lung cancer (NSCLC) patients treated with definitive chemoradiation. This prospective clinical cohort consists of unresectable, locally advanced NSCLC patients who had liquid biopsy testing prior to initiation of cancer therapy. Liquid biopsy testing was performed using a next-generation sequencing assay (MSK-ACCESS) which includes 129 genes and paired white blood cell sequencing. An FDA-recognized database (OncoKB) was utilized to classify alterations associated with radiation resistance (including KEAP1, NFE2L2, STK11, and PIK3CA) and radiation sensitivity (including ATM, ATR, BRCA1/2, ARID1A, MLH1 and other DNA Damage Repair Pathway alterations). We evaluated progression-free survival (PFS) from the completion of chemoradiation using the Log-rank test. Among 25 patients with prospective ctDNA testing prior to therapy initiation, 17 patients had stage III disease (68%), 8 patients had stage II disease (32%), 18 patients had adenocarcinoma (72%), 7 patients had squamous cell carcinoma (28%), and 23 (92%) were former or current smokers. The median radiation dose was 60 Gy in 30 fractions (range: 55 to 66 Gy in 20 to 33 fractions). 76% of patients (n = 18) had one or more alterations detected (median: 3 alterations, range: 1 - 8) including genomic markers of radiation response in 2 patients in BRCA1/2 (n = 2) and radiation resistance in 1 patient in KEAP1. The most common driver alteration detected was KRAS in 24% of the cohort (n = 6). Among patients with baseline detectable ctDNA, the median PFS was 21.3 months and was not reached among patients without baseline ctDNA detection (HR 4.54, p = 0.04). Using an institutional assay, the presence of baseline cell-free ctDNA appeared prognostic in patients with unresectable, locally advanced NSCLC treated with definitive chemoradiation. We also detected driver alterations and potential markers of radiation resistance and response using ctDNA testing. Prospective cell-free ctDNA profiling may offer pathways to therapy personalization among patients with locally advanced unresectable lung cancer.

Association of Moderate-Risk Breast Cancer Genes with Contralateral Prophylactic Mastectomy and Bilateral Disease.

The impact of ATM, CHEK2, and PALB2, the three most prevalent moderate-risk breast cancer genes, on surgical decision making is not well known. Our retrospective study included patients with resectable non-metastatic breast cancer who underwent multigene panel testing between July 2014 and January 2020 with at least one genetic alteration (pathogenic or variant of uncertain significance [VUS] in ATM [n = 49], CHEK [n = 57], or PALB2 [n = 27]). Our objectives were to determine the rate of contralateral prophylactic mastectomy (CPM) and the rate of bilateral breast cancer. Univariable analyses (UVA) and multivariable analyses (MVA) were performed to identify factors associated with CPM and bilateral breast cancer. The rate of CPM was 39% (n = 49/127), with 54% (n = 25/46) of patients with a pathogenic mutation and 30% (n = 24/81) of patients with a VUS choosing CPM. On MVA, premenopausal status (odds ratio [OR] 3.46) and a pathogenic alteration (OR 3.01) were associated with increased use of CPM. Bilateral disease was noted in 16% (n = 22/138). Patients with pathogenic mutations had a 22% (n = 11/51) incidence of bilateral breast cancer, while patients with VUS had a 13% (n = 11/87) incidence, although this was not statistically significant on UVA or MVA. On MVA, premenopausal status was associated with a decreased risk of bilateral disease (OR 0.33, p = 0.022). During follow-up, a breast cancer event occurred in 16% (n = 22/138). Our study identified a high rate of CPM among those with ATM, CHEK2, and PALB2 alterations, including VUS. Further studies are needed to clarify reasons for CPM among patients with moderate-risk alterations.

Somatic loss of ATM is a late event in pancreatic tumorigenesis.

Understanding the timing and spectrum of genetic alterations that contribute to the development of pancreatic cancer is essential for effective interventions and treatments. The aim of this study was to characterize somatic ATM alterations in noninvasive pancreatic precursor lesions and invasive pancreatic adenocarcinomas from patients with and without pathogenic germline ATM variants. DNA was isolated and sequenced from the invasive pancreatic ductal adenocarcinomas and precursor lesions of patients with a pathogenic germline ATM variant. Tumor and precursor lesions from these patients as well as colloid carcinoma from patients without a germline ATM variant were immunolabeled to assess ATM expression. Among patients with a pathogenic germline ATM variant, somatic ATM alterations, either mutations and/or loss of protein expression, were identified in 75.0% of invasive pancreatic adenocarcinomas but only 7.1% of pancreatic precursor lesions. Loss of ATM expression was also detected in 31.0% of colloid carcinomas from patients unselected for germline ATM status, significantly higher than in pancreatic precursor lesions [pancreatic intraepithelial neoplasms (p = 0.0013); intraductal papillary mucinous neoplasms, p = 0.0040] and pancreatic ductal adenocarcinoma (p = 0.0076) unselected for germline ATM status. These data are consistent with the second hit to ATM being a late event in pancreatic tumorigenesis. © 2023 The Authors. The Journal of Pathology published by John Wiley & Sons Ltd on behalf of The Pathological Society of Great Britain and Ireland.

Targeted Next-Generation Sequencing Improves the Prognostication of Patients with Disseminated Appendiceal Mucinous Neoplasms (Pseudomyxoma Peritonei).

Appendiceal mucinous neoplasms (AMNs) with disseminated disease (pseudomyxoma peritonei) are heterogeneous tumors with variable clinicopathologic behavior. Despite the development of prognostic systems, objective biomarkers are needed to stratify patients. With the advent of next-generation sequencing (NGS), it remains unclear if molecular testing can improve the evaluation of disseminated AMN patients. Targeted NGS was performed for 183 patients and correlated with clinicopathologic features to include American Joint Committee on Cancer/World Health Organization (AJCC/WHO) histologic grade, peritoneal cancer index (PCI), completeness of cytoreduction (CC) score, and overall survival (OS). Genomic alterations were identified for 179 (98%) disseminated AMNs. Excluding mitogen-activated protein kinase genes and GNAS due to their ubiquitous nature, collective genomic alterations in TP53, SMAD4, CDKN2A, and the mTOR genes were associated with older mean age, higher AJCC/WHO histologic grade, lymphovascular invasion, perineural invasion, regional lymph node metastasis, and lower mean PCI (p < 0.040). Patients harboring TP53, SMAD4, ATM, CDKN2A, and/or mTOR gene alterations were found to have lower OS rates of 55% at 5 years and 14% at 10 years, compared with 88% at 5 years and 88% at 10 years for patients without the aforementioned alterations (p < 0.001). Based on univariate and multivariate analyses, genomic alterations in TP53, SMAD4, ATM, CDKN2A, and/or the mTOR genes in disseminated AMNs were a negative prognostic factor for OS and independent of AJCC/WHO histologic grade, PCI, CC score, and hyperthermic intraperitoneal chemotherapy treatment (p = 0.006). Targeted NGS improves the prognostic assessment of patients with disseminated AMNs and identifies patients who may require increased surveillance and/or aggressive management.

Germline mutations and the presence of clonal hematopoiesis of indeterminate potential (CHIP) in 20,963 patients with BRCA-associated cancers.

10522 Background: The contribution of germline genetics on the emergence of CHIP in patients with solid tumor malignancies is not well understood. We hypothesized that those with germline (g) alterations in homologous recombination repair genes (gHRR) and BRCA-associated cancers (breast, ovarian, prostate, pancreas) would have different rates of CHIP than those without. Methods: We analyzed a large real-world Tempus multimodal database of paired germline and somatic DNA sequencing results. CHIP was calculated based on the presence of pathogenic or likely pathogenic alterations in any one of 16 CHIP-associated genes ( ASXL1, BCOR, BCORL1, CBL, CREBBP, CUX1, DNMT3A, GNB1, JAK2, PPM1D, PRPF8, SETDB1, SF3B1, SRSF2, TET2, U2AF1) with a variant allele frequency of at least 2%. Patients with g alterations in BRCA1, BRCA2, ATM, CHEK2, and PALB2 were compared to those without gHRR alterations (sporadic). Results: In breast cancer, patients with g BRCA1 (n = 104) mutations were younger (med 43 yrs) at diagnosis compared to sporadic cases (n = 6,546 med 56yrs) but had similar rates of CHIP (3% vs 5%). Those with gPALB2 (n = 42 med age 55) had the highest rate of CHIP (14%). gBRCA2 (n = 148; med age 52), gATM (n = 57 med age 52), and gCHEK2 (n = 57 med age 53) and similar rates of CHIP (3%, 4%, 7%). In ovarian cancer, patients with gBRCA1 (n = 137 med age 53) were younger at diagnosis than sporadic cases (n = 3,979 med age 63) with similar rates of CHIP (4% vs 3%). Those with gBRCA2 (n = 83 med age 61) were similar (4%) and gPALB2 (n = 11 med age 68) had the highest rate of 9%. CHIP was not detected among patients with g ATM (n = 23 med age 61) or g CHEK2 mutations (n = 9, med age 59). In prostate cancer, 4% of patients with sporadic cases had CHIP (n = 4,183 med age 66) compared to 4% in gBRCA2 (n = 109 med age 63) and 5% in gATM (n = 44 med age 66). gCHEK2 had 17% prevalence of CHIP (n = 12 med age 66) followed by gPALB2 (n = 12 med age 69). There were no CHIP mutations found among those with g BRCA1 (n = 16 med age 64). In pancreatic cancer, patients with g BRCA2 (n = 89 med age 64) and PALB2 (n = 20 med age 62) were younger at diagnosis, compared to sporadic cases (n = 5,176 med age 67) with lower rates of CHIP (1% gBRCA2, 0 PALB2, 5% sporadic). The highest proportion was in gBRCA1 patients (n = 20 med age 63) with 10%, gCHEK2 (n = 16 med age 68) with 6% and gATM (n = 60 med age 66) with 5%. Conclusions: Despite younger age at diagnosis, patients with g BRCA1 had similar or higher rates of CHIP within breast and ovarian cancer. Women with g PALB2 alterations and breast and ovarian cancer, as well as men with g CHEK2 mutations and prostate cancer, had higher rates of CHIP. These data suggest that gHRR mutations may influence the prevalence of CHIP among patients with BRCA-associated cancers and more research is needed.

A phase II study of olaparib (AZD2281) in patients (Pts) with metastatic/advanced urothelial carcinoma and other genitourinary (GU) tumors with DNA-repair defects.

TPS4607 Background: Olaparib is a poly-ADP-ribose polymerase (PARP) inhibitor that induces synthetic lethality in tumor cells with dysfunctional DNA damage repair (DDR) from loss of function of BRCA or other DDR genes. It improves survival in advanced ovarian, pancreatic, prostate and breast carcinoma with DDR gene alterations and is FDA approved for these indications. PARP inhibitors still have an undefined role in non-prostate GU tumors. We hypothesize that PARP inhibitors will have activity in DDR deficient tumors, regardless of histology. We are conducting a phase 2 trial of olaparib in non-prostate GU cancers with DDR gene defects. Methods: Eligible pts must have metastatic/advanced urothelial carcinoma or other non-prostate GU cancers and have measurable disease by RECIST 1.1. Pts in Cohorts 1 and 2 must harbor tumor or liquid pathologic DDR alterations identified by FoundationOne CDx (F1CDx) panel and reviewed by a molecular genetics review panel: Cohort 1 includes BRCA1, BRCA2, ATM, BAP1, MSH2, PALB2, and BRIP1 alterations, and pts with high tumor mutational burden (TMB) (&gt;15 mutations/megabase); Cohort 2 (exploratory cohort) includes ABL1, ATR, ATRX, BARD1, BRD4, CCND1, CHEK1, CHEK2, DOTIL, FANCC, FANCE, FANCG, FANCL, IKBKE, MEN1, MLH1, MSH2, MSH6, MUTYH, NPM1, PMS2, POLD1, POLE, RAD51, SMARCB1, STEK11, and TP53 alterations. Cohort 3 (natural history) will include pts without pathologic alterations in any Cohort 1 or 2 genes. Pts with eligible gene alterations (Cohorts 1 and 2) will be given olaparib 300mg twice daily until progressive disease, unacceptable adverse events, withdrawal of consent or death. They will have circulating tumor cells (CTCs) collected at baseline and every 4 weeks, and CT restaging every 8 weeks. Pts in Cohort 3 will receive standard of care treatment and have baseline CTC collection and be followed for survival. The primary objective is to evaluate the objective response rates (ORR) in Cohorts 1 and 2. Secondary objectives include progression-free survival (PFS), overall survival (OS) and safety. In these cohorts, the trial will have a Simon optimal two-stage design. In Cohort 1, 25 evaluable pts will be required to provide 90% power with alpha = 0.1 to differentiate between a promising ORR of 30% versus an unacceptably low ORR of 10%. In Cohort 2, 35 evaluable pts will be required to provide 90% power with alpha = 0.05 to differentiate between a promising ORR of 30% versus an unacceptably low ORR of 10%. Exploratory objectives include estimating the distribution of DDR alterations in non-prostate GU malignancies, assessing the effectiveness of NGS in detecting DDR alterations in circulating tumor DNA (ctDNA), assessing levels of baseline CTCs and changes in CTC level with olaparib, and correlating with clinical outcomes. This is an ECTCN network clinical trial and is open to enrollment. Clinical trial information: NCT03375307 .

Abstract P5-03-18: Co-occurring alterations in PALB2 germline carriers identified by liquid biopsy in patients with advanced breast cancer

Abstract Introduction: PALB2 is a BRCA complex-interacting protein and has an essential role in homologous recombination and repair (HRR). PALB2 germline (gPALB2) mutations are found in 1 – 4% of breast cancer patients and can be incidentally identified by liquid biopsy testing. Recent data has shown the efficacy for PARP inhibitors (PARPi) in breast cancer gPALB2 carriers, highlighting the importance of understanding genomic drivers in this group of patients. Here we present the genomic landscape of patients with advanced breast cancer (aBC) with incidental gPALB2 mutations identified by liquid biopsy testing. Methods: Genomic results were queried for aBC patients who had Guardant360 (G360) testing as part of routine clinical care from October 2020 – March 2022. Eligible patients had must have a diagnosis of breast cancer and an incidental gPALB2 alteration identified on G360, defined by presence of ClinVar loss-of-function single nucleotide variant (SNV)/indel mutation. Co-occurring somatic alterations in these patients were then analyzed after removing synonymous and variants of uncertain significance. Analysis of HRR-related alterations, such as loss of heterozygosity and/or copy number loss, was performed in a subset of patients. Clinical demographics and clinical status (newly diagnosed or progressing at the time of G360 testing), were extracted from test requisition forms. Results: A total of 48 patients had gPALB2 alterations: 60% had indels and 40% SNVs. gPALB2 variant allele frequencies (VAF) were &amp;gt;30% for all patients (median VAF: 49.7, range: 34.1-66.6). All patients were female with a median age of 59 years (range: 31-84); 29 (60%) were tested at progression whereas the rest were tested at diagnosis. 36 (75%) patients with gPALB2 had co-occurring somatic alterations across 23 genes. The most commonly mutated genes were TP53 (47%), ESR1 (23%), and PIK3CA (19%); other mutated genes had less than 7% frequency. Notably, 95% of patients with co-occurring ESR1 alterations and 70% found to harbor PIK3CA co-occurring alterations were tested at progression. Other clinically relevant findings include co-occurring somatic alterations in MTOR (4%) and HRR-related genes ATM, ARID1A, CHEK2, FANCA (4% each; one patient had both ATM and CHEK2 somatic alterations). No somatic BRCA1/BRCA2 alterations were identified in gPALB2 patients. For 33 (69%) patients with gPALB2, additional HRR-related biomarker analysis was performed resulting in identification of 3 (9%) patients with copy number loss, one who had CHEK2 and PALB2 single copy number loss, resulting in PALB2 biallelic loss. In the overall cohort, an additional 33 patients were identified with uniquely somatic PALB2 alterations. Conclusions: Carriers of gPALB2 alterations comprise a rare subset of aBC patients analyzed by liquid biopsy. These patients have co-occurring somatic alterations identified in genes that have been reported in published cohorts of aBC patients without gPALB2 alterations. Assessment of additional somatic HRR-related alterations may identify other patients with PALB2 findings who could benefit from PARPi. Clinical studies are needed to assess how patients with gPALB2 and co-occurring mutations may have altered response and/or resistance to therapies, including standard-of-care regimens and PARPi. Citation Format: Nan Chen, Rita Nanda, Frederick M. Howard, Neelima Vidula, Jennifer Yen, Leylah M. Drusbosky, Leslie Bucheit. Co-occurring alterations in PALB2 germline carriers identified by liquid biopsy in patients with advanced breast cancer [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P5-03-18.

Abstract P5-02-14: Identification of mechanisms of acquired resistance to ribociclib plus endocrine therapy using baseline and end-of-treatment circulating tumor DNA samples in the MONALEESA-2, -3, and -7 trials

Abstract Background: Genetic alterations that contribute to resistance to therapy may be acquired during treatment (tx) for hormone receptor−positive/human epidermal growth factor receptor−negative (HR+/HER2−) advanced breast cancer (ABC). A previous pooled analysis of circulating tumor DNA (ctDNA) in MONALEESA (ML)-2, -3, and -7 identified potential predictive biomarkers for response and resistance to ribociclib (RIB) at baseline (BL). Here, we describe an analysis of paired BL and end of treatment (EOT) samples from ML-2, -3, and -7 to identify acquired mechanisms that may impact resistance to RIB + endocrine therapy (ET) vs placebo (PBO) + ET. Methods: ML-2 (NCT01958021), ML-3 (NCT02422615), and ML-7 (NCT02278120) evaluated efficacy and safety of RIB + ET vs PBO + ET in pre- and postmenopausal patients (pts) with HR+/HER2− ABC treated in first-line (1L) and second-line (2L) settings. Plasma samples were collected at cycle 1 day 1 (C1D1; prior to first therapy exposure) and at EOT (± 28 days of recorded progression). ctDNA was sequenced using a targeted next-generation sequencing panel of ≈550 genes. Genes with an alteration frequency of &amp;gt;5% at EOT, regardless of their frequency at BL, were included. Tumor mutational burden (TMB) was assessed by tx arm; a TMB cutoff of 10 mutations/MB was used to categorize pts as TMB high vs low. To assess differences in the presence of alterations, a McNemar test was performed on paired samples and adjusted (adj) for multiple testing using the false discovery rate (FDR). A Bayesian mixed effects model was used to account for ctDNA fraction and trial and to test for tx-specific resistance by including a tx × visit interaction term. Results: A total of 905 paired samples from ML-2, -3, and -7 were included in this analysis, 441 and 464 samples from pts treated with RIB + ET and PBO + ET, respectively. Overall, 17 genes had an alteration frequency of &amp;gt;5% at EOT. The ctDNA fraction was higher at EOT vs C1D1 in both the RIB (P=.037) and PBO (P=.033) arms. The frequency of alterations in RB1 (10.4% vs 2.0%), ATM (11.3% vs 8.4%), FAT1 (4.8% vs 3.0%), and FAT3 (5.0% vs 2.5%) was higher at EOT vs C1D1 in the RIB arm (FDR-adj P&amp;lt;.10). Alterations in ESR1 were also higher at EOT vs C1D1 in both the RIB (26.3% vs 9.1%) and PBO arms (28.9% vs 5.4%) (FDR-adj P&amp;lt;.0001). Conversely, alterations in GATA3 were higher at EOT in the PBO arm (FDR-adj P=.11). These results were consistent after adjusting for ctDNA fraction. The most common ESR1 mutations were D538G, Y537S/N/C/D, E380Q, and L536H/P/R. Tx × visit interaction effects were observed for RB1 in the RIB arm and GATA3 in the PBO arm, suggesting tx-specific resistance. A tx × visit interaction for ESR1 was also observed, suggesting a larger relative increase in ESR1 mutations with PBO vs RIB. The percentage of pts with high TMB (&amp;gt;10) at EOT increased from 1.1% to 5.7% in the RIB arm and from 1.7% to 3% in the PBO arm. After accounting for ctDNA fraction and trial, a larger numerical increase in TMB was observed for RIB (odds ratio [OR], 9.0; 95% CI, 2.9-32.7) vs PBO (OR, 2.1; 95% CI, 0.7-6.5); however, the model did not support a differential tx effect. Conclusions: This comprehensive analysis of pooled samples from ML-2, -3, and -7 identified acquired gene alterations in pts with HR+/HER2− ABC treated with 1L or 2L RIB + ET or PBO + ET. The frequency of several genes known to contribute to resistance (ESR1, RB1, ATM, FAT1, and FAT3) was higher at EOT vs C1D1 in pts treated with RIB + ET, while ESR1 and GATA3 alterations were higher at EOT vs C1D1 in pts treated with PBO + ET. This paired dataset of BL and EOT samples from pts with HR+/HER2− ABC treated with a CDK4/6 inhibitor and ET is the largest to date and could be used to validate and confirm acquired resistance mechanisms with low alteration frequency. Citation Format: Fabrice Andre, Nadia Solovieff, Faye Su, Aditya Bardia, Patrick Neven, Yoon-Sim Yap, Debu Tripathy, Yen-Shen Lu, Dennis Slamon, Stephen K. Chia, Mukta Joshi, Arunava Chakravartty, Agnes Lteif, Tetiana Taran, Carlos Arteaga. Identification of mechanisms of acquired resistance to ribociclib plus endocrine therapy using baseline and end-of-treatment circulating tumor DNA samples in the MONALEESA-2, -3, and -7 trials [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P5-02-14.

Abstract P3-05-10: Disease features, genomic profiles and outcomes of younger vs. older Chinese hormone receptor positive (HR+), HER2 negative (HER2-) metastatic breast cancer (MBC) patients

Abstract Background: Breast cancer in younger women has been characterized as a more aggressive disease with relatively poor outcomes compared to breast cancer in older women. This pattern has been attributed to a variety of clinicopathologic characteristics including the enrichment of aggressive HER2+ and TNBC subtypes in younger patients. However, similar to older breast cancer patients, the majority of young breast cancer patients are HR+/HER2-. Here we have evaluated the clinicopathologic characteristics and genomic profiles of real-world HR+/HER2- MBC patients to examine the determinants of outcome for younger vs. older patients in this subtype. Patients and Methods: This study included 65 Chinese patients presenting with HR+/HER2- MBC at the Peking University Cancer Hospital. Blood samples were collected upon metastatic disease diagnosis before treatment and profiled with the targeted 152-gene PredicineCARETM sequencing panel. Fourteen patients were &amp;lt; 40 years, 19 were 40-50 years, and 32 were &amp;gt; 50 years at the time of primary cancer diagnosis. Kaplan-Meier survival analysis was performed to analyze outcomes including overall survival (OS), disease free survival (DFS) and progression free survival (PFS) in association with clinicopathologic and genomic variables. OS was also evaluated in association with age in separate multivariate models using Cox proportional hazards regression. Results: Significant variation across age groups was observed for several clinicopathological features, including molecular subtype classification (p = 0.045), de novo Stage IV disease (p = 0.011), type of adjuvant endocrine therapy (p = 5.56E-06), resistance to adjuvant endocrine therapy (p = 0.015) and receipt of adjuvant chemotherapy (p = 0.042). Luminal B status was most frequent in patients &amp;lt; 40 years (92.31%), whereas de novo Stage IV disease was more prevalent in patients &amp;gt; 50 years (37.5%). Aromatase inhibitors (AIs) were administered as adjuvant endocrine therapy (ET) to 73.68% of women &amp;gt; 50 years vs. 16.67% and 0% of women aged 40-50 years and &amp;lt; 40 years, respectively. Resistance to adjuvant ET was observed in 23.08% of patients &amp;lt; 40 years but was not observed in the other age groups. Adjuvant chemotherapy was received by a higher proportion of patients in the 40-50 year age group (94.44%) compared to patients &amp;lt; 40 years (69.23%) and patients &amp;gt; 50 years (60%). No differences in somatic gene alteration frequencies were observed across age groups, menopausal status, germline mutation status or tumor grade. However, a higher frequency of FGFR1 alterations was observed in patients classified as Luminal B vs. A (p = 0.048). Comparison of profiles across women who received adjuvant ET revealed a higher prevalence of FGFR1 (p = 0.012), ATM (p = 0.047) and CCND2 (p = 0.04) alterations in patients treated with AIs vs. SERMS. In addition, a higher frequency of APC alterations was observed in patients with high (≥ 20%) vs. low (&amp;lt; 20%) Ki67 index (p = 0.035). At the univariate level OS was significantly associated with age (p = 0.039). OS was shortest in patients &amp;gt; 50 years, intermediate in patients &amp;lt; 40 years, and longest in patients 40-50 years. Across all patients, shorter OS was also associated with de novo Stage IV disease (p = 0.0001), Luminal B subtype (p = 0.008), adjuvant ET with AIs vs SERMS (p = 0.028) and the presence of an FGFR1 (p = 0.028) or CCND2 (p = 0.033) alteration. In multivariate analyses, OS remained significantly longer for patients aged 40-50 years after adjustment for de novo Stage IV disease, Luminal B subtype and FGFR1 status (all p &amp;lt; 0.05). Conclusions: In this group of real-world HR+/HER2- MBC breast cancer patients, younger age was not associated with worse outcomes. While current guidelines recommend treatment decisions based on tumor biology rather than age, young HR+ breast cancer patients are more likely to receive chemotherapy. Our findings support the development of biomarker-driven treatment strategies for these patients. Citation Format: Jinhao Wang, Yaxin Liu, Bin Shao, Hang Dong, Tiantian Zheng, Pan Du, Shidong Jia, Bonnie King, Jing Wang, Xiaoran Liu, Huiping Li. Disease features, genomic profiles and outcomes of younger vs. older Chinese hormone receptor positive (HR+), HER2 negative (HER2-) metastatic breast cancer (MBC) patients [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P3-05-10.