BRCA Wt Research Articles

LBA58 - BAROCCO: A randomized phase II study of weekly paclitaxel vs cediranib-olaparib combination given with continuous or intermittent schedule in patients with recurrent platinum resistant ovarian cancer (PROC)

BackgroundHypoxia induced by antiangiogenic agents could cause a functional impairment of homologous recombination, thus sensitizing wild-type (wt) BRCA tumor cells to PARP inhibition. In a phase II study the combination of cediranib-olaparib increased progression free survival (PFS) in women with recurrent platinum sensitive OC with respect to olaparib. Methods123 patients were allocated in a 1:1:1 ratio to receive: 80mg/m2 weekly paclitaxel up to 24 weeks (control), olaparib 600mg tablet (300mg twice daily) together with 20mg cediranib daily (continuous schedule) or 20mg cediranib given 5 days/week (intermittent schedule) until progression. PFS comparison between experimental schedules and the control arm (alpha one-sided 5%; power 80% to detect a HR of 0.5) was the primary objective. ResultsMedian platinum-free interval was 1.8 mos, 59% of patients were pretreated with >3 chemotherapy lines. Median PFS for paclitaxel, the continuous, and the intermittent schedules were 3.1, 5.7, and 3.8 mos. Estimated HR for PFS in continuous arm vs control was 0.76 (90% CI: 0.49-1.17), p=0.28 by log-rank test. HR for PFS in intermittent arm vs. control was 1.08 (90% CI: 0.71-1.64), p=0.76 by log-rank test. In the subgroup gBRCA wt (n=109) the median PFS for paclitaxel, the continuous, and the intermittent schedules were 2.1, 5.8 and 3.8 mos and HR for PFS in continuous arm vs control was 0.63 (95% CI: 0.36 to 1.10; p=0.10). The toxicity profile of the study arms was as expected and similar between experimental arms. 11%, 18%, and 7% in control, continuous and intermittent arm discontinued treatment for adverse events. Five serious adverse drug reactions occurred and two of these were fatal: one in the control and one in the continuous arm. ConclusionsThe combination of cediranib and olaparib is effective in heavily pretreated PROC patients with the advantage of an oral administration and good tolerability. The continuous schedule of cediranib-olaparib showed a promising trend towards improved PFS in comparison with weekly paclitaxel particularly in the BRCA wt population. Clinical trial identificationIRFMN-OVA-7289, EudraCT: 2016-003964-38, NCT03314740. Legal entity responsible for the studyIstituto di Ricerche Farmacologiche Mario Negri IRCCS. FundingAstraZeneca. DisclosureN. Colombo: Honoraria (self), Advisory / Consultancy: Roche/Genentech; Honoraria (self), Advisory / Consultancy: PharmaMar; Honoraria (self), Advisory / Consultancy: AstraZeneca; Honoraria (self), Advisory / Consultancy: Tesaro; Advisory / Consultancy: Clovis Oncology; Advisory / Consultancy: Pfizer; Advisory / Consultancy: MSD Oncology; Advisory / Consultancy: BioCad; Advisory / Consultancy: Takeda. G. Tognon: Advisory / Consultancy: Amgen; Speaker Bureau / Expert testimony, Research grant / Funding (institution): Roche; Speaker Bureau / Expert testimony, Research grant / Funding (institution): AstraZeneca; Speaker Bureau / Expert testimony: Tesaro. M. Ratti: Travel / Accommodation / Expenses: Tesaro Bio. All other authors have declared no conflicts of interest.

184PD - Neoadjuvant olaparib monotherapy in primary triple negative breast cancer

BackgroundNeoadjuvant treatment of triple negative breast cancer (TNBC) in general implies different chemotherapy regimens administered in sequence. PARP inhibitors like olaparib have revealed clinical benefit in TNBC harboring BRCA germline mutations, but were ineffective when tested as monotherapy for BRCA WT metastatic breast cancer. While combining a PARP inhibitor with chemotherapy may be beneficial, such therapy is limited by bone marrow toxicity. MethodsIn the phase 2 PETREMAC trial (NCT02624973), we assessed the efficacy of primary olaparib monotherapy for 10 weeks, followed by chemotherapy, in TNBC (T>2cm). Tumor biopsies and blood leucocytes for targeted DNA sequencing of 360 cancer-related genes were collected prior to therapy and after 10 weeks on olaparib. Results31 patients with TNBC were included (mean tumor size 59mm; range 33-97). Olaparib monotherapy was well tolerated, yielding a clinical CR in 5 and a PR in 15 patients (all-over objective response rate; ORR 64%). Olaparib had no major impact on subsequent chemotherapy toxicity. The average pretreatment mutation rate was 3.3 indels/point mutations per tumor with no differences in mutation burden recorded between responders and non-responders or BRCA carriers vs. non-carriers. Among five patients harboring pathogenic BRCA1/2 mutations (4 germline, 1 somatic) all responded to olaparib, and n=3/5 obtained pathological complete response. Interestingly, mutations in genes associated with DNA damage repair (ATRX, BRCA1/2, EMSY, MSH6, PARP10, PPM1D) occurred in n=9/20 olaparib responders, but in none of the 11 non-responders (p=0.011). Non-responders were characterized by mutations in oncogenic pathways (PIK3CA, AKT1, KRAS, IGF2R, NF2 and TGFBR2) in 7 out of 11 tumors (P=0.00013). No significant association was observed between TP53 mutations (recorded in 23/31 tumors) and response to olaparib. Targeted DNA sequencing is ongoing for biopsies taken after 10 weeks of olaparib monotherapy; the results will be presented. ConclusionsOlaparib yielded a high response rate when administered to treatment-naïve, large TNBC, indicating a potential role in sequential neoadjuvant therapy, for patients both with and without BRCA1/2 germline mutations. Clinical trial identificationNCT02624973; 2015-002816-34. Legal entity responsible for the studyHaukeland University Hospital, Bergen, Norway. FundingDet Regionale Samarbeidsorganet/Helse Vest, AstraZeneca. DisclosureH.P. Eikesdal: Honoraria (self), Research grant / Funding (institution), Travel / Accommodation / Expenses: AstraZeneca; Honoraria (self), Advisory / Consultancy, Research grant / Funding (institution): Novartis; Honoraria (self), Advisory / Consultancy, Speaker Bureau / Expert testimony, Research grant / Funding (institution): Pfizer; Honoraria (self), Travel / Accommodation / Expenses: Pierre Fabre; Honoraria (self): Amgen; Honoraria (self), Advisory / Consultancy: Roche; Honoraria (self): HAI Interaktiv AS; Honoraria (self): Dagens Medisin; Honoraria (self): Brysol-Mayers-Squibb; Advisory / Consultancy: Lilly; Research grant / Funding (institution): Abbvie. E.S. Blix: Honoraria (self): Pfizer. B. Gilje: Honoraria (self), Advisory / Consultancy, Research grant / Funding (self): Roche; Honoraria (self), Research grant / Funding (institution): AstraZeneca; Advisory / Consultancy, Research grant / Funding (institution): Astellas Oncology; Research grant / Funding (institution): Celgene; Research grant / Funding (institution): Pfizer; Travel / Accommodation / Expenses: Pierre Fabre. E.A. Janssen: Honoraria (self): AstraZeneca; Honoraria (self): Pfizer. J. Geisler: Honoraria (self), Advisory / Consultancy, Speaker Bureau / Expert testimony: Novartis; Honoraria (self), Advisory / Consultancy, Speaker Bureau / Expert testimony: MSD; Honoraria (self), Advisory / Consultancy: Lilly; Honoraria (self), Speaker Bureau / Expert testimony: Pierre Fabre; Honoraria (self), Speaker Bureau / Expert testimony: Brystol-Myers-Squibb; Advisory / Consultancy, Speaker Bureau / Expert testimony: AstraZeneca; Speaker Bureau / Expert testimony: Pfizer. T. Aas: Honoraria (self): AstraZeneca; Honoraria (self): Roche. S. Knappskog: Honoraria (self), Research grant / Funding (institution): AstraZeneca; Honoraria (self), Research grant / Funding (institution): Pfizer; Licensing / Royalties: Patent EP2389450 A1,Patent WO 2012/010661.. P.E. Lønning: Honoraria (self), Advisory / Consultancy, Research grant / Funding (institution): AstraZeneca; Research grant / Funding (self): Pfizer; Research grant / Funding (self): Novartis; Honoraria (self), Travel / Accommodation / Expenses: Pierre Fabre; Honoraria (self): Roche; Advisory / Consultancy: Laboratorios Farmaceuticos Rovi; Licensing / Royalties: Cytovation. All other authors have declared no conflicts of interest.

Clinical significance of pathogenic variants in germline BRCA wild type patients at risk for hereditary breast cancer.

e13127 Background: Approximately, 10% of breast cancer (BC) are related to inherited germline mutations. BRCA1/2, the most recognized and tested genes, are responsible for 50% of hereditary BC. Genetic testing for hereditary BC has changed significantly. Increasing evidence suggests parallel multigene testing. Methods: NGS-based germline BRCA status assessment was performed on 209 high risk BC patients with at least one of the following risk factors: triple negative BC, early onset ( < -45), with a family history of BC, bilateral BC and male BC. Multigene-panel testing was subsequently offered to patients with at least 2 of the risk factors and WT germline BRCA. Capture-base targeted sequencing was performed on white blood cells using a panel consisting of 53 hereditary cancer-related genes, spanning 229kb of human genome. Results: Among the 209 patients screened, only 12 patients had pathogenic BRCA1/2 mutation. Next, we investigated the prevalence of non- BRCA pathogenic germline pathogenic mutations in patients with at least 2 risk factors. Thirty-seven patients met the criteria and only 23 patients had sufficient WBC DNA for sequencing. This cohort had a median age of 42, with a majority carrying infiltrating ductal carcinoma. Except for one bilateral BC patient who had stage IV disease, all other patients had early stage disease. We identified 5 pathogenic mutations from 5 patients spanning 4 genes: PALB2, PTEN, ATM and WRN, resulting in a prevalence rate of 20% for pathogenic germline mutations in high risk germline BRCA WT BC patients. Two patients carried mutations in PALB2, one with a frameshift and another with a splice mutation. Mutation types for PTEN, ATM and WRN were splice mutation, stop gain mutation and frameshift mutation, respectively. All 5 patients were diagnosed with BC before the age of 40. Three of them had bilateral BC; one had triple negative BC and another patient had a family history of BC. Conclusions: Our study confirms the clinical significance of testing non- BRCA genes, and suggests multigene panel testing for patients at risk for hereditary BC. Such approach increases the identification of hereditary BC, thus impacting clinical decision-making.

Abstract P4-22-21: NCI9782: A phase 1 study of talazoparib in combination with carboplatin and paclitaxel in patients with advanced solid tumors

Abstract Background: Poly(ADP-ribose) polymerase (PARP) enzymes are involved in DNA repair and activated by DNA strand breaks. DNA damage from carboplatin is associated with activation of PARP. Preclinical data indicate that PARP inhibition potentiates the anti-tumor effect of platinum chemotherapy. Talazoparib (T) is an oral, selective PARP inhibitor with a single agent maximum tolerated dose (MTD) of 1mg orally qd. Primary dose-limiting toxicity (DLT) was thrombocytopenia. This phase I study combines T with the commonly used chemotherapy regimen of carboplatin (C) and paclitaxel (P). Methods: Two dosing schedules are being investigated. In both schedules, C is administered on day 1 and P on days 1, 8, and 15 of a 21-day cycle. T (100-1000mcg) is dosed once daily for days 1-7 (schedule A) or days 1-3 (schedule B) starting on day 1. A 3+3 design is used for dose escalation. Key eligibility criteria include age 318 with a measurable or evaluable solid incurable malignancy. Patients (pts) must have tumor type that is expected to respond to C + P or have BRCA germline or somatic mutation. Stable, treated brain metastases are allowed. No prior C for metastatic disease is allowed. Pts must have platelets>150 and no need for anticoagulation. After 4-6 cycles of combination therapy, pts may continue the combination, change to C and intermittent T without P or change to T alone with continuous daily dosing. Each schedule will have a 6 subject dose expansion at the MTD. The starting dose level for schedule B will be the MTD from schedule A. Results: Schedule A cohort results are reported: 11 pts (median age 59 [range 39-68]; 8 female; 3 male) have been enrolled. Pts had breast (6), ovarian (2), pancreatic (1), and SCC of oropharynx (1) and concurrent ovarian and pancreatic (1). Five pts are BRCA2+ and 3 pts are BRCA1+. Dose level 3 on schedule A (T 350mcg with C AUC 6 and P 80mg/m2) exceeded the MTD with 2 of 3 pts experiencing hematologic dose limiting toxicities (DLTs) including 1 pt with grade (gr) 3 neutropenic fever and gr 4 thrombocytopenia and another pt with grade 3/4 neutropenia lasting > 7 days. Most common AEs include neutropenia (grade 3-4: 7), anemia (grade 3-4: 3), and thrombocytopenia (grade 3-4: 4). Results from expansion of dose level 2 (T 250mcg with C AUC 6 and T 80mg/m2) will be presented. The 11 pts were on study a median of 9 weeks (range 9-36+). Four pts have discontinued study therapy: 1 due to need for anticoagulation for PE, 1 for prolonged cytopenias, and 2 for disease progression. Of the 8 pts with measurable disease evaluated for response to date, 4 had SD, 1 had a cPR, 1 had radiographic CR, and 2 with PD. A pt with BRCA 1+ triple negative breast cancer has maintained a prolonged PR (36+ weeks) even after dose reductions to T 100mcg with C AUC 3. One pt with ovarian cancer (BRCA WT) has radiographic CR (CA 125 remains mildly elevated) after 15+ weeks of therapy. Conclusion: PARP inhibition with talazoparib days 1-7 in combination with carboplatin and paclitaxel leads to DLT of myelosuppression. However, clinical responses are seen even with lower dose combinations. Citation Format: Turk A, Chan N, Leal T, O'Regan R, Tevaarwerk A, Rice L, Campbell T, Barroilhet L, Mehnert J, Eickhoff J, Kolesar J, Liu G, Wisinski K. NCI9782: A phase 1 study of talazoparib in combination with carboplatin and paclitaxel in patients with advanced solid tumors [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P4-22-21.

Abstract P2-04-19: Elucidating the tumor immune microenvironment phenotype in early stage untreated BRCA mutated breast cancer patients

Abstract Background: Increased stromal tumor infiltrating lymphocytes (TILs) are predictive and prognostic for improved outcomes from neoadjuvant or adjuvant chemotherapy in triple negative breast cancer. Increased tumor mutational burden may promote neoantigens causing immune system upregulation. Microsatellite instability in gastrointestinal cancer predicts for response to checkpoint inhibition and is associated with inherited cancer predisposition. The immune system response in BRCA mutated breast cancer has not been described. The purpose of this study is to assess tumor infiltrating immune cells in early stage breast cancer patients with and without BRCA gene mutations. Methods: We retrospectively investigated 124 early stage breast cancer patients with BRCA mutations (n=62, BRCA+) and without BRCA mutations (n=62, BRCA WT). The %TILs was measured manually by H&E. Our control group consisted of age, stage, and receptor status matched early stage untreated breast cancer patients who were deemed BRCA WT by extended gene panel testing or were negative for BRCA 1/2 and had a posttest probability of harboring an autosomal dominant mutated gene of ≤ 1% using the Bayes-Mendel algorithm. We used a two-sample binomial arcsin approximation to detect a 20% difference in TILs between cohorts to attain 80% power with a one-side alpha of 0.05. Wilcoxon Rank-Sums test was used to compare differences in the central tendencies for continuous variables. We used the Nanostring PanCancer immune profiling panel to immunophenotype a portion of the BRCA+ and BRCA WT cohorts and used nSolver for quality control, normalization, and bioinformatics analyses. Results: Here we report TILs from the first 21 patients of our study. Thirteen patients harbored BRCA mutations and eight patients did not. All patients were HER2 negative. Eight (61%) and four (50%) patients were hormone receptor positive (HR+) in the BRCA+ and BRCA WT cohorts, respectively. Median %TILs were not significantly different between the BRCA+ (15, range 0-70) and BRCA WT (17.5, range 5-60; p=0.7) groups. Median %TILs in the HR+/BRCA+ (12.5, range 0-50) and HR-/BRCA+ (15, range 5-70) cohorts were not statistically different when compared to HR+/BRCA WT (10, range 5-15; p=0.4) and HR-/BRCA WT (30, range 20-60; p=0.2) cohorts, respectively. There were 2 patients with lymphocyte predominant breast cancer (n=1, HR-/BRCA+; n=1, HR-/BRCA WT). Conclusions: This is the first study to characterize TILs and a tumor immune microenvironment phenotype in early stage breast cancer patients with BRCA mutations. These results suggest harboring a BRCA mutation is not associated with increased TILs in early stage untreated breast cancer patients. This conclusion stayed true regardless of hormone receptor status. However, a trend of decreased TILs was seen in HR-/BRCA+ patients when compared to those with HR-/BRCA WT disease. Moreover, the median and range of TILs were higher in the HR+/BRCA+ group compared to the HR+/BRCA WT group. This suggests increased TILs may exist in some HR+ patients with a BRCA mutation. Further investigation of TILs and immune profiling of early stage untreated breast cancer patients with and without BRCA mutations is warranted. Citation Format: Force J, Abbott S, Broadwater G, Kimmick G, Westbrook K, Hwang S, Kauff N, Stashko I, Weinhold K, Nair S, Hyslop T, Blackwell K, Castellar E, Marcom PK. Elucidating the tumor immune microenvironment phenotype in early stage untreated BRCA mutated breast cancer patients [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P2-04-19.

Abstract P2-04-04: BRCA gene mutations do not shape the extent and organization of tumor infiltrating lymphocytes in triple negative breast cancer

Abstract The remarkable responses observed in metastatic cancer patients treated with immunotherapies, including inhibitors directed to the PD-1 and PD-L1 checkpoint molecules, makes it a priority to identify critical variations in pro- and anti-tumor immune responses in breast cancer (BC). In patients with triple negative (TN) BC, an increased presence of tumor infiltrating lymphocytes (TIL) and tertiary lymphoid structures (TLS) have been associated with good clinical outcomes. However, the frequency of specific lymphocyte subpopulations, PD-1 and/or PD-L1 expression and their prognostic significance remains an open question. Our recent work found that PD-1 and PD-L1 expression are specifically associated with higher TIL densities and an increased number of TLS in BC. We further demonstrated that TIL density, TLS and PD-L1 expression were correlated with more aggressive breast tumor characteristics, including higher proliferation and hormone receptor negativity. In this project, we examined the prevalence of TIL, TLS, PD-1 and PD-L1 expression in TNBC and further compared these immune parameters between TNBC patients harboring BRCA1 or BRCA2 germline gene mutations with those carrying the wild-type (wt) genes. A total of 1402 BC patients whose blood was genetically tested for germline BRCA1 and BRCA2 mutations were examined for inclusion in this study. Ninety-eight chemotherapy-naïve patients with primary invasive ER–, PR– and HER2– BC and demonstrated germline BRCA1 or BRCA2 wt or mutated-gene status were included in this study. Ninety-four tumors were determined to be suitable for evaluating immune cell infiltration (51 BRCA wt and 43 BRCA-mutated). FFPE tumor tissue from the surgical specimens was analyzed by immunohistochemistry (IHC) staining of full-face tissue sections. IHC was performed as a dual label using CD3 plus CD20 for T and B cells, CD4 plus CD8 for the major T cell subpopulations and PD-1 plus PD-L1 for individual or paired expression of these receptors. The stained slides were independently scored by two experienced pathologists for TIL, TIL subpopulations, TLS and checkpoint molecule expression. These analyses revealed that 87% of our TNBC cohort was TIL-positive (≥10% TIL) with 35% classified as lymphocyte predominant BC (LPBC; ≥50% TIL). T cells were the principal component of the lymphocytic infiltrate with no significant differences between the BRCA wt and BRCA-mutated groups detected in total T cells (CD3+), helper T cells (CD4+), cytotoxic T cells (CD8+) or B cells (CD20+). TLS were identified in 73% of tumors with again no significant differences between the BRCA groups. Examination of checkpoint molecule expression identified 33% tumors as PD-1 positive and 40% as PD-L1 positive. PD-1 expression was correlated with PD-L1 expression and both with TIL positivity and the level of immune infiltration but not BRCA mutational status. Overall, our analyses revealed that BRCA wt and BRCA-mutated TNBC are remarkably similar in terms of TIL heterogeneity, a TLS presence and checkpoint molecule expression. These data suggest that BRCA gene mutations are not immunogenic nor do they directly drive immune infiltration in TNBC. Citation Format: Willard-Gallo K, Solinas C, Marcoux D, t'Kint de Roodenbeke D, Garaud S, Van den Eynden G, de Wind A, Boisson A, Larsimont D, Piccart M. BRCA gene mutations do not shape the extent and organization of tumor infiltrating lymphocytes in triple negative breast cancer [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P2-04-04.

Highly favorable outcome in BRCA-mutated metastatic breast cancer patients receiving high-dose chemotherapy and autologous hematopoietic stem cell transplantation.

Breast cancer carrying BRCA mutation may be highly sensitive to DNA-damaging agents. We hypothesized a better outcome for BRCA-mutated (BRCA(mut)) metastatic breast cancer (MBC) patients receiving high-dose chemotherapy and autologous hematopoietic stem cell transplantation (HDC AHSCT) versus unaffected BRCA (BRCA wild type; (BRCA(wt))) or patients without documented BRCA mutation (BRCA untested (BRCA(ut))). All female patients treated for MBC with AHSCT at Institut Paoli-Calmettes between 2003 and 2012 were included. BRCA(mut) and BRCA(wt) patients were identified from our institutional genetic database. Overall survival (OS) was the primary end point. A total of 235 patients were included. In all, 15 patients were BRCA(mut), 62 BRCA(wt) and 149 BRCA(ut). In multivariate analyses, the BRCA(mut) status was an independent prognostic factor for OS (hazard ratio (HR): 3.08, 95% confidence interval (CI): 1.10-8.64, P=0.0326) and PFS (HR: 2.52, 95% CI :1.29-4.91, P=0.0069). In this large series of MBC receiving HDC AHSCT, we report a highly favorable survival outcome in the subset of patients with documented germline BRCA mutations.

Abstract B50: Antineoplastic activity of Top I inhibitor etirinotecan pegol (NKTR-102) and PARP inhibitor rucaparib (CO-388) in platinum-resistant high-grade serous BRCA WT ovarian cancer PDX models.

Abstract Background: At the time of ovarian cancer platinum resistance, standard therapies have limited activity. New anti-cancer drug combinations may lead to improved clinical outcomes. Activity of topoisomerase I (Top I) inhibitors or poly(ADP-ribose) polymerase (PARP) inhibitors have been reported in ovarian cancer and have demonstrated potentiation in other models. Objective: To investigate the efficacy of the Top I inhibitor etirinotecan pegol (NKTR-102) and the PARP inhibitor rucaparib (CO-338) as single agents and in combination in patient-derived xenograft (PDX) models of ovarian cancer. Methods: Five ovarian cancer PDX models in SCID mice were treated for 28 days with NKTR-102 (10 mg/kg/q7d IV), rucaparib (150 mg/kg/qd PO), or combination NKTR-102 plus rucaparib at the same doses and schedules. Of the five PDX models, four were platinum resistant and one was a platinum-sensitive positive control. Each treatment arm had a total of 10 mice and animals were observed daily for body weight and general condition. Tumor size was assessed weekly by ultrasound. The primary endpoint was change in tumor cross-sectional area (cm2) from pretreatment baseline to final tumor burden. Western blot was performed to investigate potential biomarkers of response. Results: Compared to vehicle-treated controls, statistically significant improvement (p<0.05) was observed in 3 of 5 models in single agent rucaparib treated tumors and in 5 of 5 models in single agent NKTR-102 treated tumors. The combination of NKTR-102 plus rucaparib also demonstrated statistically significant improvement compared to vehicle-treated controls in 5 of 5 models. The combination of NKTR-102 plus rucaparib induced maximal tumor regression in 2 of 5 tumors with a trend towards smaller tumors compared to single agent treatment arms. This was not found to be statistically significant in the 28 day study period under which the experiment was performed. Exploratory analysis to assess candidate drug response determinants (e.g.Top I, PAPR I, and PARP polymer formation levels) was investigated. Conclusion: NKTR-102 and rucaparib are well tolerated in mice and demonstrate activity in platinum-resistant and platinum-sensitive ovarian cancer PDX models. Combination therapy demonstrated a trend towards decreased tumor size when compared to single agent activity during treatment. Current efforts are focused on extending the time on study for the PDX models evaluated to determine if statistical superiority of the NKTR-102/rucaparib combination can be established. Citation Format: Caroline C. Nitschmann, Rachel M. Hurley, Marc A. Becker, Xiaonan Hou, Ute Hoch, Thomas C. Harding, Deborah H. Charych, Scott H. Kaufmann, Paul Haluska, Saravut J. Weroha. Antineoplastic activity of Top I inhibitor etirinotecan pegol (NKTR-102) and PARP inhibitor rucaparib (CO-388) in platinum-resistant high-grade serous BRCA WT ovarian cancer PDX models. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Ovarian Cancer Research: Exploiting Vulnerabilities; Oct 17-20, 2015; Orlando, FL. Philadelphia (PA): AACR; Clin Cancer Res 2016;22(2 Suppl):Abstract nr B50.

Abstract 4226: Histone deacetylase inhibitors sensitize cancer stem cells to PARP inhibitors in triple-negative breast cancer

Abstract Background: Triple negative breast cancers (TNBCs) have a poor prognosis and are a therapeutic challenge due to resistance to multiple chemotherapy drugs. Growing evidence suggests that cancer stem cells (CSCs) may be promising therapeutic targets for treating TNBCs. Poly ADP ribose polymerase (PARP) inhibitors have shown striking activity in preclinical models of BRCA-deficient breast carcinomas. However they are less efficacious in tumors without germline BRCA mutations, which account for more than 80% of all TNBCs. Our data demonstrates that treatment of TNBC with PARP inhibitor increases CSCs, likely due to an elevated homologous recombination (HR) repair mechanism. Several small studies have suggested that histone deacetylase (HDAC) inhibitors, which decrease HR repair proteins, may sensitize non-BRCA-mutated TNBC to PARP inhibitors. Currently, little is known whether this synergistic effect can reverse the increase in CSCs caused by PARP inhibition. In this study, our aim was to investigate if HDAC inhibitors could sensitize CSCs to PARP inhibitors in TNBCs. Results: Using four TNBC cell lines, we confirmed the synthetic lethality of HDAC and PARP inhibitors (Vorinostat and Olaparib respectively) in vitro. CompuSyn analysis revealed Combination Indices of 0.66, 0.44, 0.47 and 0.16 in SUM159, MDAMB231, SUM149 and HCC1937 cells respectively at ED50. An ALDEFLUOR assay revealed ∼1.9 fold increase in the CSC population after PARP inhibition in BRCA-mutant SUM149 and HCC1937 cells, while the absolute CSC number, (total cell number times percentage of ALDEFLUOR-positive cells) remained unchanged. Whereas in BRCA-wild type TNBC cell lines SUM159 and MDAMB231, there was no change in CSCs. Addition of the HDAC inhibitor decreased absolute CSC number by 85%, 78% and 40% in SUM149, SUM159 and HCC1937 cells respectively after 7 days of PARP inhibition. Although the mechanism is not fully understood at present, we demonstrated that Rad51, a key player in HR repair, mediates the sensitivity of TNBCs to PARP inhibition, and HDAC inhibitor prevents the formation of Rad51 foci at DNA damage site. This may indicate that HDAC inhibition sensitizes the CSCs of TNBCs to PARP inhibition via suppressing the HR pathway. Conclusion: Our data suggests that PARP inhibition only targets the bulk cancer cells in BRCA-mutant TNBC cells while sparing CSCs and has no effect on BRCA WT cells. HDAC inhibition sensitized CSCs of TNBC to PARP inhibition regardless of BRCA status, possibly via interfering with Rad51 function. The inhibitors we used in the present study are either FDA-approved or at Phase III clinical trials, and the combination is predicted to have low toxicity. Thus, our findings are promising and could be rapidly translated into clinical use. Citation Format: Yajing Liu, Rachel Martin-Trevino, Li Shang, April Davis, Max Wicha, Suling Liu, Monika Burness. Histone deacetylase inhibitors sensitize cancer stem cells to PARP inhibitors in triple-negative breast cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4226. doi:10.1158/1538-7445.AM2015-4226

Assessment of γH2AX levels in circulating tumor cells in patients treated with veliparib in combination with doxorubicin and cyclophosphamide in metastatic breast cancer.

2582 Background: Veliparib (V) is a potent PARP inhibitor that delays repair of DNA damage induced by chemotherapeutic agents. In metastatic breast cancer pts, we evaluated V with doxorubicin (A) and cyclophosphamide (C) given both on day 1 with V at 100 mg po BID for 7 days post-chemotherapy every 21 days, to increase DNA damage. We report use of γH2AX, (phosphorylated histone protein), a marker of DNA double-strand breaks, in circulating tumor cells (CTCs) to assess DNA damage. We evaluated number of CTCs and percentage of γH2AX-positive CTCs pre- and post-treatment. Methods: Eligibility included prior A ≤ 300 mg/m2 and EF ≥ 50%. Further A was omitted after a cumulative dose of 420 mg/m2. Primary objective was to assess DNA damage response to treatment by measuring γH2AX-positive CTCs during cycle 1 on days 1 (pre-treatment), 2, 7, and 14. Cell Search System was used to enumerate CTCs. γH2AX was quantitated using a validated assay. Results: Eleven pts enrolled. Median age was 53 (34 – 73); median ECOG PS 1 (0 – 2); there were 1 ER-negative/HER2+, 4 triple-negative (BRCA2+, n =1), and 6 ER+/PR+/HER2-negative (BRCA2+, n =2) tumors. Most common drug-related toxicities were grade (gr) 4 neutropenia, gr 2 anemia and thrombocytopenia, and gr 1 nausea and vomiting. In BRCA2+ pts, there were 2 PRs and 1 SD. In BRCA wt or unknown status, 5 pts had SD ≥ 3 mo and there were 3 PDs. CTCs (≥ 8) were detected in 10/11 pts on days 1 and 2. Day 7 samples were not obtainable in 2 pts. On day 7, 1/8 pts had 0 CTCs and rest had ≥ 3 CTCs. A decrease in CTCs (p < 0.0001) occurred from day 1 (median: 22, range, 8-1216) to day 7 (median: 5, range 3-37). At baseline, 7 pts had ≥ 10% γH2AX-positive CTCs. Fraction of CTCs positive for γH2AX increased to ≥ 50% by day 7 in 6/7 pts and persisted to day 14 in 5 pts. Conclusions: The toxicity profile of V 100 mg BID days 1-7 with AC (60/600 mg/m2) on day 1 on a 21-day cycle was expected. Objective antitumor activity was seen in BRCA mutation carriers. CTCs decreased and percentage of γH2AX-positive CTCs increased after combination treatment with a PARP inhibitor and chemotherapy. This observation is notable and we plan to extend dosing of V to 14 days. This work is supported by NCI U01-CA132194. Clinical trial information: NCT00740805.

Abstract PD09-03: Impact of BRCA1/2 Mutation Status in TBCRC009: A multicenter phase II study of cisplatin or carboplatin for metastatic triple negative breast cancer.

Abstract Background: Triple negative breast cancer (TNBC) has a poor prognosis compared to other BC subtypes and lacks identified specific therapeutic targets. TNBC is frequent among BRCA1-associated breast cancer. Platinum chemotherapy has activity in TNBC, and several studies have suggested particular efficacy of platinum agents in BRCA-associated breast cancer. TBCRC009 is a multicenter single arm phase II study of single agent platinum in metastatic TNBC. Here we sought to evaluate the impact of BRCA1/2 mutation status on outcomes in this study population. Methods: Eligible metastatic TNBC patients (pts) had measurable disease, available archival tumor, ≤ 1 prior metastatic therapy, and no prior platinum chemotherapy. Pts were assigned by physician choice (limited to equal enrollment in each arm) to cisplatin 75mg/m2 or carboplatin AUC=6 every 21 days with optional extension to 28 days after cycle 1. Co-primary endpoints were: 1) Response Rate (RR) and 2) whether tumor p63/p73 expression predicts response. Secondary endpoints included determination of BRCA1/2 mutation status and exploratory analysis of correlation of BRCA1/2 status with outcomes. Baseline blood samples from all pts were analyzed by Myriad Genetics using BRCAnalysis and BART testing. Results of this exploratory analysis are presented here. Results: 86 TNBC pts enrolled between June 2007-Oct 2010. Results of primary endpoint 1 and patient characteristics were previously presented (ASCO 2011 Annual Meeting, J Clin Oncol 29: 2011 suppl; abstr 1025). In summary, median age=52 (30–78), 64% had ECOG PS=0, and 86% had adjuvant chemotherapy. Overall response rate (RR) was 30.2% (95% CI 20.8%–41.1%), including 4 CR (4.7%), 22 PR (25.6%). Among the 76 pts with BRCA1/2 status available, there were 11 (14.5%) BRCA1/2 carriers (9 BRCA1, 2 BRCA2) and 65 (85.5%) BRCA1/2 wild type (wt). Testing is ongoing for the remaining 10 pts. RR was 54.6% (5 PR, 1 CR) in BRCA1/2 carriers and 26.2% (14 PR, 3 CR) in BRCA1/2 wt (p = 0.0506). There was no significant difference in PFS between BRCA1/2 carriers (median PFS 99 days; 95% CI: 40–215) and BRCA1/2 wt (median PFS 86 days, 95% CI: 46–146). Interestingly, 6 pts (7%), including 5 BRCA1/2 wt and 1 BRCA unknown, remain without progression for 53, 41, 33, 27, 25, and 22 months as of June 2012. Of these 6 pts, 3 pts discontinued study drug due to toxicity and received no additional therapy and 3 pts had major responses and had consolidation therapy with surgery, chemotherapy, or radiation. Conclusion: First or second line single agent platinum is effective in both BRCA1/2-associated and sporadic metastatic TNBC. In this exploratory analysis, we observed a higher RR in BRCA1/2 carriers than in BRCA wt patients, but we did not observe an improved PFS in this small cohort. We observed durable responses in 7% of pts which did not correlate with BRCA1/2 mutations. The lack of a clear relationship between the higher RR in patients with germline BRCA1/2 mutations and PFS is surprising and could be further elucidated by studies in a larger cohort, and our ongoing analyses of additional markers for platinum sensitivity. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr PD09-03.