Prior Chemotherapy Exposure Research Articles

“Synchronous Development of Acute Myeloid Leukemia and Multiple Myeloma: A Rare Case Presentation”

Abstract Introduction/Objective The co-occurrence of acute myeloid leukemia (AML) and multiple myeloma (MM) presents a diagnostic challenge, particularly when it arises without prior chemotherapy exposure. This study aims to elucidate the clinical characteristics, diagnostic approach, and management implications of such synchronous hematologic malignancies through a detailed case report. Methods/Case Report A 64-year-old female with no previous medical history presented with chest pain, shortness of breath, and hematologic abnormalities. Clinical evaluation revealed severe pancytopenia, cystic liver mass, enlarged retroperitoneal lymph nodes, and hypercalcemia. Peripheral blood smear indicated hematologic malignancy, prompting further investigation. Bone marrow aspirate analysis, including flow cytometry and immunohistochemical stains, was performed to confirm the dual cell populations of AML blasts and MM plasma cells. Results (if a Case Study enter NA) Flow cytometric analysis and immunohistochemical stains of the bone marrow aspirate confirmed the presence of distinct cell populations: blasts expressing markers consistent with AML and abundant plasma cells indicative of MM. Monotypism of plasma cells was established, with kappa predominance. Notably, there was no coexpression of markers between the AML blasts and MM plasma cells. Conclusion This case highlights the rare occurrence of synchronous AML and MM in a patient without prior chemotherapy exposure. The diagnostic approach involving flow cytometry and immunohistochemical stains proved essential in confirming the dual hematologic malignancies. Clinicians should be vigilant for such presentations, as timely diagnosis and appropriate management are crucial for optimizing patient outcomes in these complex cases.

GOG3069: Phase 2 study of alpelisib and fulvestrant for PIK3CA-mutated estrogen receptor (ER)-positive endometrioid endometrial cancers.

TPS5639 Background: Treatment options for persistent, metastatic, or recurrent endometrial cancer continues to evolve as we learn more about the molecular landscape of this disease. Recent studies have shown a benefit to endocrine-based combinations such as aromatase inhibitors with mTOR or CDK4/6 inhibitors especially in patients who had not received prior chemotherapy ( 1– 3). The presence of oncogenic PIK3CA mutations have been shown to impact response to aromatase inhibitors in breast cancer. The combination of alpelisib and fulvestrant was approved for the treatment of metastatic hormone receptor-positive, HER2-negative breast cancer harboring oncogenic mutations in the PIK3CA gene that progressed on prior endocrine therapy( 4). PIK3CA mutations are commonly identified in endometrial cancers and may similarly confer endocrine resistance. GOG3069 is a phase II trial designed to evaluate the efficacy and safety of alpelisib and fulvestrant in a biomarker-selected endometrial cancer patient population. Methods: This is a phase II non-randomized, open label, multicenter, two-stage study. Eligible patients must have advanced (FIGO 2014 Stage III or IV), persistent, or recurrent endometrial carcinoma with measurable disease by RECISTv1.1 criteria. Patients cannot be curable by surgery or radiotherapy. Disease must be of endometrioid histology with positive expression of estrogen receptor (defined as ≥1% of tumor cells demonstrating positive nuclear staining by immunohistochemistry) and oncogenic PIK3CA mutation. Patients may have received no more than 3 prior lines of therapy including 1 prior line of systemic chemotherapy. Enrolled patients will receive treatment with alpelisib 300mg orally daily and fulvestrant 500mg IM on Day 1 and Day 15 of Cycle 1, then 500mg IM on Day 1 of each 28-day cycle. The primary endpoint is overall response rate as measured by RECISTv1.1-defined tumor response. Secondary endpoints include safety, tolerability, progression-free survival, duration of response, and 24-month overall survival rate. GOG3069 activated in November 2023 and expects to enroll across 15 US sites. The statistical plan uses a conditional stratified design factoring differing probabilities of response based on whether the patient had prior chemotherapy exposure. ClinicalTrials.gov Identifier: NCT05154487

Risk of secondary leukemias in patients with germline PALB2 pathogenic variants after chemotherapy exposure.

10598 Background: Pathogenic variants in germline cancer-predisposing genes (e.g. BRCA1/2, PALB2) confer an increased risk for solid tumors but not de novomyeloid malignancies. Many of these genes are related to DNA repair pathways. It is not known whether exposure to genotoxic therapy increases the risk of secondary hematologic malignancies. Here, we report the incidence of hematologic malignancy after a solid tumor diagnosis among patients with a germline PALB2 pathogenic variant. Methods: Patients were identified at the Massachusetts General Hospital Center for Cancer Risk Assessment among individuals seeking counseling and/or testing for hereditary cancer risk genes. Analyses were conducted using R version 4.2.2 “tidyverse” and “gtsummary” packages. Results: Of the 176 charts reviewed, 102 (57%) had a history of malignancy, of which 68 (66%) received genotoxic chemotherapy. The median follow-up after chemotherapy was 59mo (IQR =17,109). The most common malignancy and chemotherapy were breast cancer (n=76, 75%) and doxorubicin, cyclophosphamide, and paclitaxel (n = 21, 31%). We compared patient outcomes by receipt of chemotherapy or not. There was no difference in race, age at cancer diagnosis, surgery rate, treatment with hormone therapy, or secondary malignancy between the two groups (p > 0.05). There was higher incidence of radiation treatment in those receiving genotoxic therapy compared to those who did not (65% vs 41%, p = 0.024), but no difference Gray or in follow up after radiation. Mortality in the genotoxic therapy group was 15% (n=10) vs. 9% (n=2) in the no genotoxic therapy group (p =0.33). Two subjects developed a hematologic malignancy (one case each of CLL and CML); both had prior chemotherapy and radiation exposure (Table). Conclusions: Cancer survivors with a germline PALB2 pathogenic variant and subsequent exposure to genotoxic therapy appear to have low risk of secondary hematologic malignancy. Although two subjects in the chemotherapy group developed leukemias, given the cases seen it is unlikely that these relate to the treatment exposure. Given the small sample size and retrospective nature of this study, more investigation is necessary to fully quantify the risk of therapy-related myeloid neoplasm in patients with germline PALB2 pathogenic variants. [Table: see text]

Generation and assessment of cytokine-induced killer cells for the treatment of colorectal cancer liver metastases

Colorectal cancer (CRC) is the second leading cause of cancer-related death worldwide. Cytokine-induced killer (CIK) cells are an adoptive immunotherapy reported to have strong anti-tumour activity across a range of cancers. They are a heterogeneous mix of lymphoid cells generated by culturing human peripheral blood mononuclear cells with cytokines and monoclonal antibodies in vitro. In this study, we investigated the yield and function of CIK cells generated from patients with CRC liver metastases. We first showed that CIK cells generated in serum free medium X-VIVO 15 were comparable to those from RPMI medium with 10% FBS in terms of the number and percentages of the main subsets of cells in the CIK culture, and the intracellular levels of granzyme B and perforin, and the pro-inflammatory cytokines IL-2, IFN-γ and TNF-α. The CIK cells were cytotoxic to CRC cell lines grown in 2D cultures or as spheroids, and against autologous patient-derived tumour organoids. Donor attributes such as age, sex, or prior chemotherapy exposure had no significant impact on CIK cell numbers or function. These results suggest that functional CIK cells can be generated from patients with CRC liver metastatic disease, and support further investigations into the therapeutic application of autologous CIK cells in the management of patients with CRC liver metastases.

Alterations in Immune Cell Composition during First-Line Therapy with Mosunetuzumab for Follicular or Marginal Zone Lymphoma

Background: Bispecific CD20xCD3 antibodies (BiAbs) that engage T-cells to eliminate CD20+ B-cells have emerged as a potent immunotherapy for the treatment of follicular (FL) and marginal zone (MZL) lymphomas. BiAbs have primarily been studied in patients with extensive prior immunosuppressive and lymphodepleting therapies, so their effects on the immune system without such exposures are not well understood. Unlike cellular therapies, BiAbs are administered continuously over time, spanning from 6 months to an indefinite period, and recent studies have raised concerns about T-cell exhaustion due to continuous BiAb exposure in B-lymphoblastic leukemia (Philipp et al, Blood 2022). Mosunetuzumab is a BiAb approved for treatment of relapsed/refractory FL. The ongoing phase 2 BrUOG-401 trial (NCT04792502) is investigating mosunetuzumab as first-line therapy for FL or MZL. Here, we present preliminary results focusing on treatment-induced changes in circulating immune cells. Methods: Patients with previously untreated, high-burden or symptomatic FL or MZL received subcutaneous mosunetuzumab for 8 planned cycles (C) with step-up dosing in C1 (day 1: 5mg, day 8 & 15: 45 mg; then 45mg on day 1 of C4-C8). Patients without a complete response (CR) at interim assessment after C4 also received lenalidomide augmentation (10mg daily) during C5-8. Immune cell subsets were examined using multicolor flow cytometry (BD LSRII Analyzer). Peripheral blood samples were collected longitudinally before C1, on day 1 of C2 and C5, and 4-6 weeks after the end of therapy (EOT). Median cell abundance and marker expression were compared using generalized linear mixed models with patient and sample-level random effects. Analysis was performed in R (v.4.3.1) using the flowCore, flowStats and diffcyt packages; uncorrected P<0.05 was considered statistically significant. Results: As of July 2023, 13 patients (median age 62, 77% women, 77% FL, 23% MZL) were accrued in the trial. At data cutoff, 7 have completed therapy, 11 were evaluable for response, and 8 attained CR ( Fig. A). So far, only 1 patient started lenalidomide; samples collected while on lenalidomide were excluded from analysis. No instances of cytokine release syndrome (CRS) or neurotoxicity were observed. CR's occurred early (by C5). Mosunetuzumab resulted in a rapid, deep, and sustained depletion of circulating CD19+ B-cells. A significant decrease in circulating CD8+ T-cells was noted at cycle 2 (from median 20% to 12%, P<0.001; Fig. B), followed by recovery (19% at C5). Among the CD8+ subsets, the naïve CD8+ T-cells (CD45RA+CCR7+CD27+) decreased relatively at C5 & EOT, while effector memory T-cells (CD45RA-CD45RO+CD27-CD62L-) increased. Notably, we observed a significant early, temporary, increase in the expression of LAG3 at C2 on CD8+ T-cells ( P=0.033), and a more pronounced increase in PD1 expression ( P=0.001), which persisted through the EOT ( Fig. B). No significant changes were observed in total abundance of CD4+ T-cells. However, CD4+CD25+CD127- Tregs notably increased at C2 ( P=0.008). This increase specifically driven by CD45RA+ “naïve” Tregs ( P<0.001 at C2), which remained elevated relative to CD45RO+ Tregs at C5 and EOT. All Tregs showed a significant increase in LAG3 expression at C2 ( P<0.001), which then subsided. In contrast to CD8+ T-cells, there was no significant increase in PD1 expression on CD4+ T-cells ( P=0.20 at C2). Throughout the therapy, there was a progressive increase in NK cells ( P=0.001 at EOT), with no significant shift in the relative proportions of CD16high or CD161high NK cells. Conclusions: In this initial investigation of immune cell changes in patients who received mosunetuzumab without prior chemotherapy exposure, we observed B-cell depletion and a temporary decrease in CD8+ cytotoxic T-cells (implying their migration out of the bloodstream), aligning with mosunetuzumab's mechanism of action. Additional data from this trial will aid in understanding whether the persistent increase in PD1+CD8+ T-cells and expansion of Tregs are linked to a functionally exhausted phenotype and whether lenalidomide could potentially reverse it. Although our observation is limited by sample size, it can still provide insights into optimizing the administration schedules of BiAb therapy in future trials (e.g., intermittent vs. continuous) or determining the most suitable timing for checkpoint inhibitor combinations.

Intensive Induction Chemotherapy Vs Hypomethylating Agents + Venetoclax (HMA/VEN) in NPM1-Mutant Newly Diagnosed Acute Myeloid Leukemia (AML) - a Multicenter Cohort Study

Introduction: Intensive induction chemotherapy (IC) with cytarabine + anthracycline remains the standard of care for younger and fit patients (pts) with acute myeloid leukemia (AML). Post-hoc analyses from clinical trials evaluating venetoclax (VEN)-based therapies in AML have identified mutations in NPM1 as being associated with high rates of durable responses. However, these trials were conducted in pts age ≥75 years or unfit for IC. Thus, it is unknown whether IC or hypomethylating agent (HMA)+VEN is the optimal frontline treatment for pts with NPM1-mutant AML. We performed a large multicenter retrospective cohort study dedicated to pts with newly diagnosed AML with NPM1 mutations, comparing treatment modalities and assessing the impact of clinical and molecular characteristics on response and survival. Methods: We included pts with newly diagnosed, NPM1-mutant AML who were treated at 4 large academic centers with IC (either conventional 7+3 or liposomal cytarabine/daunorubicin [CPX-351]) or HMA+VEN. Detection of NPM1 mutations was performed at the participating sites either by polymerase chain reaction (PCR) or next-generation sequencing (NGS) per local standards. Composite complete response (cCR) was defined as complete response (CR) + CRi (CR with incomplete count recovery) per European LeukemiaNet 2017 criteria. Overall survival (OS) was compared between groups by log-rank test. Cox regression multivariable model for OS was fitted using a stepwise backward selection to evaluate the effect of treatment, allogeneic stem cell transplantation (allo-SCT) as a time-varying covariate and additional covariates with a p<0.1 in the univariate model. Results: We reviewed 1132 pts with AML and included 225 pts with NPM1-mutant AML in the final analysis ( Table 1). Among these pts, 71% (n=160) and 29% (n=65) received IC and HMA+VEN, respectively. Some pts (22%) in the IC group also received midostaurin compared to 0% in the HMA+VEN group. Pts who received IC for NPM1-mutant AML were younger (median age 61 years [Range: 22 -76] vs 74 years [33 -89]; p<0.001) when compared to HMA+VEN and less likely to have prior myelodysplastic syndrome (MDS) or myeloproliferative neoplasms (MPN; 10% vs 20%, p=0.042), and SF3B1 mutations (3.1% vs 15%; p=0.002). There was no difference in the rate of FLT3-ITD mutations between groups (36% vs 29%; p=0.36). Rates of cCR and CR were higher for IC than HMA+VEN-treated pts (cCR: 87% vs 74%; p=0.018; CR: 83% vs 52%; p<0.001), as well as rates of allo-SCT (56% vs 23%; p<0.001). Median OS was 31 months (95% CI: 24 months [mo] - not reached [NR]) for the total cohort of pts with NPM1-mutant AML and was better in pts treated with IC vs HMA+VEN (IC: 24 mo OS 65% [95% CI: 57 - 74%] vs HMA+VEN: 24 mo OS 38% [95% CI: 26 - 55%]; p<0.001). While the median OS remained favorable for IC among pts age > 60 years with NPM1-mutant AML (34 mo [95% CI: 24 mo - NR] vs 15 mo [13 mo - 28 mo]; p=0.015), there was no difference in OS by treatment type among the pts undergoing allo-SCT (IC: median OS not reached; 24 mo OS: 72% [95% CI: 63-83%] vs HMA+VEN: median OS 29 mo; 24 mo OS 69% [95% CI: 48-100%]; p=0.55). In the univariate analysis, treatment (HMA+VEN vs IC), age, prior chemotherapy exposure, abnormal cytogenetics, SF3B1, TET2 and RNA splicing mutations were associated with worse outcomes ( Table 2). Of note, neither the presence of concurrent FLT3 or IDH1/2 mutations nor allo-SCT as a time-varying covariate had a statistically significant impact on OS. In the multivariable analysis, treatment with HMA+VEN vs. IC retained its predictive value (hazard ratio: 2.00; 95% CI: 0.92 - 3.03; p=0.006), as well as prior chemotherapy and abnormal cytogenetics ( Table 2). Conclusion: In pts with newly diagnosed NPM1-mutant AML, treatment with IC was associated with higher cCR rates and favorable OS when compared with HMA+VEN in multivariable regression analysis. However, as residual confounding cannot be excluded given the significant differences in baseline patient and disease characteristics between the two groups, a randomized clinical trial is needed to definitively verify the potential superiority of IC vs HMA+VEN in pts with newly diagnosed NPM1-mutant AML.

Mutational Changes in Solid Cancer Cells Induce DNA Damage Repair Deficiency in Hematopoietic Cells Leading to a Distinct Spectrum of Clonal Hematopoiesis Independent from Age-Related Clonal Hematopoiesis

Clonal hematopoiesis (CH) is characterized by the acquisition of defined somatic mutations in hematopoietic stem cells (HSC). It is well known that CH contributes to the development of hematological malignancies but also increases the risk of developing non-malignant conditions such as cardiovascular, pulmonary, and inflammatory liver disease. However, less is known about the association between clonal hematopoiesis and solid cancer. Reports suggest that patients with solid cancer have a higher incidence of clonal hematopoiesis at an earlier age and an inferior prognosis. To investigate whether the presence of solid cancer itself can drive the development of clonal hematopoiesis, we analyzed 392 paired tumor and blood samples from patients with advanced cancer. In our cohort, all patients had evidence of clonal hematopoiesis based on a variant allele frequency (VAF) of at least 2%. With respect to a defined set of the 20 most frequently CH-associated genes, we discovered an increased CH rate of 23% of all patients (90 cases, median age of 61 years, defined by a VAF from 2% to 30%). The frequency of mutated genes differed greatly from published data from the general population and cancer patients, with the most common mutations being PABPC1 (39%), KMT2C (28%), RUNX1 (18%), and DNMT3A (10%). In addition, we observed a strong correlation between certain mutations in tumor samples and the frequency of CH. The mutational signature of CH was not mainly associated with a typical chemotherapy-dependent mutational signature, but with an impaired DNA repair capacity. For further investigation, we performed additional experiments in mice, which showed that the presence of malignant cells impairs DNA repair capacity in HSC through inflammatory changes in the stroma. In summary, we were able to show that patients with advanced or recurrent solid tumors have a significantly increased frequency of CH, which is not only the result of prior chemotherapy exposure but the result of diminished DNA repair capacity. This suggests a possible role of solid cancer in promoting the development of CH independent from chemotherapy exposure, which is supported by our additional murine experiments.

BCRP drives intrinsic chemoresistance in chemotherapy-naïve breast cancer brain metastasis.

Although initially successful, treatments with chemotherapy often fail because of the recurrence of chemoresistant metastases. Since these tumors develop after treatment, resistance is generally thought to occur in response to chemotherapy. However, alternative mechanisms of intrinsic chemoresistance in the chemotherapy-naïve setting may exist but remain poorly understood. Here, we study drug-naïve murine breast cancer brain metastases (BCBMs) to identify how cancer cells growing in a secondary site can acquire intrinsic chemoresistance without cytotoxic agent exposure. We demonstrate that drug-naïve murine breast cancer cells that form cancer lesions in the brain undergo vascular mimicry and concomitantly express the adenosine 5'-triphosphate-binding cassette transporter breast cancer resistance protein (BCRP), a common marker of brain endothelial cells. We reveal that expression of BCRP by the BCBM tumor cells protects them against doxorubicin and topotecan. We conclude that BCRP overexpression can cause intrinsic chemoresistance in cancer cells growing in metastatic sites without prior chemotherapy exposure.

SABRSeq: A Randomized Phase Ib Trial of SABR Sequencing with Pembrolizumab in Metastatic Non-Small Cell Lung Cancer (NSCLC)

The optimal sequencing of stereotactic ablative body radiotherapy (SABR) with anti-PD1 checkpoint blockade is unknown. The purpose of SABRseq was to assess the toxicity of the combination of SABR delivered either before or after the commencement of pembrolizumab. The central hypothesis is that the treatment combination will have a safety profile that is clinically acceptable and demonstrate anti-tumor efficacy. Furthermore, we hypothesize that differences in systemic immune activation will be observed between treatment arms. This was a single institutional phase Ib randomized clinical trial (Trial ID NCT03307759). Eligible patients had metastatic NSCLC, ECOG performance 0-1, and had not received prior checkpoint immunotherapy, high-dose radiation (>36 Gy) within 6 months, or either systemic or radiation therapy within 4 weeks of randomization. Eligible patients had either TPS≥50% PD-L1 expression in the first-line or TPS≥1% PD-L1 expression with prior chemotherapy exposure. Patients were randomized to SABR before the commencement of pembrolizumab [ARM1] or SABR commencing after pembrolizumab [ARM2]. SABR was delivered in a single fraction of 18-20 Gy to 1-3 lesions. The primary endpoint was treatment-related adverse events (AE's) related to SABR and/or pembrolizumab. Secondary endpoints included best overall response (BOR), overall survival (OS), and progression-free survival (PFS). Translational objectives included the evaluation of longitudinal changes in immunological cellular subsets within peripheral blood to explore changes in systemic immunity and circulating tumor DNA (ctDNA) dynamics. Between December 2017 and December 2019, 13 patients were randomized. The median follow-up was 37 months. The study was closed early due to poor accrual. Median age was 66 years, with 11 patients (84%) having adenocarcinoma. Nine (69%) were enrolled in the first-line setting. The median [range] number of lesions was 6 [3-11]. The median [range] cycles of pembrolizumab delivered in ARM 1 was 13 [12-32] and ARM 2 was 9 [3-34]. Grade 3 treatment-related AEs were experienced in 0 of 5 patients in ARM1 and in 1 of 8 patients in ARM 2 (hyperglycemia). There were no grade 4 or 5 adverse events reported. The BOR by both RECIST and iRECIST criteria was CR in one patient, PR in seven patients, SD in five patients. Median (95% Cis) PFS was 12.4 months (6.3-21.0), and median (95% Cis) OS was 47.1 months (12.6-not reached; 2-year point estimate 62% [31-82]). Mass cytometry was used on serial peripheral blood samples to examine changes in the frequency of immune cells, changes in T cell activation, differentiation and functional polarization state. Targeted sequencing was performed to assess ctDNA. Translational outcomes will be presented. There was no evidence of a concerning safety signal from either SABR before or after start of pembrolizumab. The combination demonstrated activity with promising PFS and OS and is worthy of evaluation in larger randomized trials.

BRCA1/2 MUTATIONS IMPACT ON THE DEVELOPMENT OF BREAST IMPLANT‐ASSOCIATED LYMPHOMA (BIA‐ALCL) IN WOMEN WITH BREAST CANCER RECONSTRUCTED WITH TEXTURED BREAST IMPLANTS

Introduction: Breast Implant-associated anaplastic large cell lymphoma (BIA-ALCL) is a subtype of T-cell lymphoma arising as a seroma and/or mass in relation to the capsule of textured breast implants. Previous research in a Dutch population suggests a higher-than-expected prevalence of BRCA1/2 carriers in women with BIA-ALCL. Here we analyze the risk of BIA-ALCL occurrence related to BRCA in a large population of women with implants followed long term after breast cancer (BC) mastectomy. Methods: We compared the prevalence of BRCA1/2 pathogenic variants (pv) between women from a large cohort of BC patients treated at Memorial Sloan Kettering Cancer Center (MSKCC) who did and did not develop BIA-ALCL after reconstruction with textured implants. Hazard ratios (HRs) of developing BIA-ALCL were estimated using Cox regression. To best control for age at BC diagnosis and length of follow up, we conducted a nested case-control within the cohort, matching 1:3, analyzed with conditional logistic regression. Results: Among 3312 women with BC assessed for pv in the context of MSK-IMPACT tumor and normal study at MSKCC the prevalence of BRCA mutations was 5.3%. Among 526 patients with textured implants post BC mastectomy, followed long term at MSKCC (median FU 82 mo, range 12, 316) and clinically assessed for BRCA1/2, the prevalence of pv of BRCA1/2 was 7.8%. Of 31 BIA-ALCL post-BC cases seen at MSKCC, 16 received capsulectomy at MSKCC and 5/13 (38.4%) were BRCA1–2 positive. Within the cohort of 526 patients with BC tested for BRCA, reconstructed with textured implants and followed long-term, the age-adjusted rate of developing BIA-ALCL for women with BRCA mutations was 11.0 times the rate of BIA-ALCL among women without BRCA (HR 95% CI 3.6, 33.9, p < .0001). Carrying bilateral versus unilateral implants (HR 6.9, 95% CI 0.9, 53.2), prior chemotherapy exposure (HR 0.7, 95% CI 0.2, 2.05), prior radiation therapy exposure (HR 0.5, 95% CI 0.1, 2.5) were not significantly associated with the rate of BIA-ALCL. Within this cohort, 13 BIA-ALCL cases were matched 1:3 with 39 controls. Median ages at BC mastectomy were 47.2 (37, 66) and 46.8 (35, 65) in cases and controls, respectively. The median time between reconstruction for BC and BIA-ALCL was 130 (80, 190) months. The odds ratio of BIA-ALCL associated with carriership of a BRCA1/2 pathogenic variant was 12.4 (Wald 95% CI 1.4, 109.5 p = 0.0074). Conclusions: In this study, we define the role of BRCA1/2 mutations as a significant risk factor in the development of BIA-ALCL in patients with BC reconstructed with textured implants. These results will help decision making for women with BRCA1/2 mutations undergoing breast reconstruction, or with textured implants in place. Analysis of pathogenic variants in other DNA repair genes in this cohort potentially affecting lymphomagenesis is ongoing. The research was funded by: NIH R03 grant number R03CA267435 Keywords: aggressive T-cell non-Hodgkin lymphoma, prevention and cancer interception No conflicts of interests pertinent to the abstract.

Concurrent chemo-hormonal therapy of enzalutamide (ENZ) and cabazitaxel (CAB) in patients (Pts) with metastatic castration-resistant prostate cancer (mCRPC): Final analysis of objective response rate (ORR), radiographic progression-free survival (rPFS), and overall survival (OS).

5047 Background: We previously reported the PSA response rate and toxicity data of a phase 1/2 single-arm, multi-institutional trial to examine the efficacy and safety of co-administration of ENZ + CAB in mCRPC without prior chemotherapy given in the mCRPC setting. We found that full doses of ENZ (160 mg daily) and CAB (25 mg/m2) were tolerable and that 80% of pts had PSA decline ≥50%. Here, we report the final analysis of ORR, rPFS and OS. Methods: We calculated the ORR (CR/PR) and 95% confidence intervals using the Clopper-Pearson Exact Method. We determined response according to RECIST 1.1 for measurable disease and Prostate Cancer Working Group 2 criteria for non-measurable (bone) disease. We estimated median rPFS (time from the study entry to the time of confirmed progression (radiographic or clinical) or death) and OS (time from the study entry to death) with 95% confidence intervals using the Kaplan-Meier method; data cutoff was 6/1/22. Statistical analysis was performed using R: A language and environment for statistical computing. Results: 37 pts consented and 35 were included in the efficacy analyses (1 withdrew consent, 1 was lost to follow up before efficacy assessment); 7/35 (20%) had prior exposure to chemotherapy given for mHSPC and 9/35 (25%) had prior exposure to abiraterone (ABI), including 2/35 (25.7%) with prior exposure to chemotherapy and ABI. 28 pts had at least one on-study trial imaging study and were evaluable for ORR. After a median follow-up of 23.7 (range: 4.9 to 62.4) months (mo), median OS was 25.1 mo (95%CI 19.4 - 37.6 mo). Median PSA PFS was 11.9 mo (95%CI 9.2 - 15.4), and median rPFS was 22.2 mo (95%CI 13.6 - 25.2). PK assessments revealed that ENZ decreased CAB levels: CAB (monotherapy) Cmax 178.9ng*h/ml vs CAB (in the presence of ENZ) Cmax 85.5 ng*h/ml (p&lt;0.05). Conclusions: The combination of ENZ+CAB in this heterogeneous mCRPC population, which included about a quarter of pts with prior chemotherapy and ABI exposure, resulted in an OS of 22.5 mo comparing favorably with the OS of 25.2 mo seen in the FIRSTANA trial of single agent CAB in docetaxel naïve men, 15.1 mo post chemotherapy in the TROPIC trial, and 13.6 mo in the post-docetaxel, post-ABI in the CARD trial. Of note, the rPFS in this trial was 22.2 months compared to 5.1 months in FIRSTANA suggesting improved efficacy; however cross-trial comparisons are discouraged due to several confounders. Chemo-hormonal therapies and prognostic/predictive biomarkers warrant further study in mCRPC. Clinical trial information: NCT02522715 . [Table: see text]

The microtubule inhibitor eribulin demonstrates efficacy in platinum-resistant and refractory high-grade serous ovarian cancer patient-derived xenograft models.

Despite initial response to platinum-based chemotherapy and PARP inhibitor therapy (PARPi), nearly all recurrent high-grade serous ovarian cancer (HGSC) will acquire lethal drug resistance; indeed, ~15% of individuals have de novo platinum-refractory disease. To determine the potential of anti-microtubule agent (AMA) therapy (paclitaxel, vinorelbine and eribulin) in platinum-resistant or refractory (PRR) HGSC by assessing response in patient-derived xenograft (PDX) models of HGSC. Of 13 PRR HGSC PDX, six were primary PRR, derived from chemotherapy-naïve samples (one was BRCA2 mutant) and seven were from samples obtained following chemotherapy treatment in the clinic (five were mutant for either BRCA1 or BRCA2 (BRCA1/2), four with prior PARPi exposure), recapitulating the population of individuals with aggressive treatment-resistant HGSC in the clinic. Molecular analyses and in vivo treatment studies were undertaken. Seven out of thirteen PRR PDX (54%) were sensitive to treatment with the AMA, eribulin (time to progressive disease (PD) ⩾100 days from the start of treatment) and 11 out of 13 PDX (85%) derived significant benefit from eribulin [time to harvest (TTH) for each PDX with p < 0.002]. In 5 out of 10 platinum-refractory HGSC PDX (50%) and one out of three platinum-resistant PDX (33%), eribulin was more efficacious than was cisplatin, with longer time to PD and significantly extended TTH (each PDX p < 0.02). Furthermore, four of these models were extremely sensitive to all three AMA tested, maintaining response until the end of the experiment (120d post-treatment start). Despite harbouring secondary BRCA2 mutations, two BRCA2-mutant PDX models derived from heavily pre-treated individuals were sensitive to AMA. PRR HGSC PDX models showing greater sensitivity to AMA had high proliferative indices and oncogene expression. Two PDX models, both with prior chemotherapy and/or PARPi exposure, were refractory to all AMA, one of which harboured the SLC25A40-ABCB1 fusion, known to upregulate drug efflux via MDR1. The efficacy observed for eribulin in PRR HGSC PDX was similar to that observed for paclitaxel, which transformed ovarian cancer clinical practice. Eribulin is therefore worthy of further consideration in clinical trials, particularly in ovarian carcinoma with early failure of carboplatin/paclitaxel chemotherapy.

A Phase I/II Study of Combination of Azacitidine, Venetoclax and Pevonedistat in Patients with Newly-Diagnosed Secondary Acute Myeloid Leukemia (AML) and Myelodysplastic Syndrome (MDS) with Hypomethylating Agent (HMA) Failure

Background: Pevonedistat (PEV) is an inhibitor of NEDD8-activating enzyme (NAE) which is critical for degradation of several cellular proteins essential for tumor growth and survival. The combination of azacitidine (AZA) and venetoclax (VEN) is approved for patients (pts) with newly diagnosed (ND) AML who are unsuitable for intensive chemotherapy, and clinical studies show preliminary efficacy with AZA+VEN in higher risk MDS pts. We evaluate the efficacy and safety of the combination of AZA, VEN, and PEV in ND secondary AML (s-AML) and in MDS after HMA failure. Methods: This phase 1/2 trial enrolled pts with ND s-AML, including therapy-related AML (t-AML), AML from prior MDS or chronic myelomonocytic leukemia (CMML) or myeloproliferative neoplasm (MPN), or AML with dysplasia in ≥50% cells in ≥2 myeloid lineages (MRC). A second arm enrolled pts with MDS or CMML that had progressed on prior HMA therapy. Pts had to have a performance status ≤2, total bilirubin ≤1.5 x upper limit of normal (ULN), ALT/AST ≤2.5 x ULN, and creatinine clearance ≥30 mL/min. Pts in AML arm may have received prior HMA for preceding hematologic malignancy. In both AML and MDS/CMML cohorts, pts received AZA 75 mg/m2 SC/IV on days 1-7 and PEV 20 mg/m2 IV on days 1, 3 and 5 on every 28 day-cycle. In AML cohort, VEN was given on days 1-28 in cycle 1 and days 1-21 on cycle 2+. In MDS/CMML cohort, VEN was given on days 3-14 in cycle 1 and days 1-14 on cycle 2+. In initial phase 1 portion of the study (AML cohort only), VEN at max dose 200 mg and 400 mg were explored. Results: Between 3/2019 and 8/2021, 32 pts with AML (10 t-AML, 22 AML from MDS/CMML/MPN, 4 MRC) and 8 pts with MDS/CMML post-HMA failure (6 with MDS, 2 with CMML) were treated (Table). In the AML cohort, the median age was 74 years, with 14 pts (44%) ≥75 years of age. Cytogenetics was adverse in 21 pts (66%), and adverse risk mutations, including TP53, RUNX1, and ASXL1 were present in 34%, 31%, and 22%, respectively. 17 pts (53%) had treated secondary AML (ts-AML; i.e. prior exposure to HMA or chemotherapy for preceding myeloid neoplasm). The overall response rate (ORR, defined as CR+CRi+MLFS) was 75%, with CR in 15 pts (47%), CRi in 6 pts (19%), and MLFS in 3 pts (9%). One pt achieved PR (3%). 78% of pts achieved best response after 1 cycle of therapy (range, 1-4 cycles to best response). Among 21 pts with CR/CRi, 10 pts (48%) achieved MRD negativity by flow cytometry. 14/21 pts (67%) with poor-risk cytogenetics responded, compared to 10/11 pts (91%) with non-poor cytogenetics. 9/11 pts (82%) with TP53-mutated AML responded. 11/17 pts (65%) with ts-AML responded, compared with 13/15 pts (87%) who did not have ts-AML. With median follow up of 20 months (mos) for the AML cohort, the median OS was 8.2 mos and median relapse-free survival (RFS) was 7.4 mos. 5 pts proceeded to transplant in first remission. The median OS for pts with adverse cytogenetics was 6.8 mos and was not reached in pts without adverse cytogenetics (1-year OS of 70%). The median OS for pts with TP53-mutated AML (n=11) was 8.1 mos, pts with inv(3) (n=4) was 3.8 mos, and pts without TP53 mutation or inv(3) (n=17) was 18 mos (Figure). In MDS/CMML HMA failure cohort, the median age was 73 years. Most pts had adverse cytogenetics (50%) and were high to very high-risk by IPSS-R (87%). Overall response rate (CR+marrow CR [mCR]+HI) was 75%, with CR in 3 pts (37%), mCR in 2 pts (25%), and HI in 1 pts (13%). With a median follow up of 11 mos, the median OS was 9.9 mos. Transformation to AML occurred in 1 pt (after 11 mos). No DLTs were observed in the phase 1 portion, and VEN 400 mg daily was the recommended phase 2 dose. Myelosuppression was similar to expectations with AZA+VEN alone. Grade 3/4 non-hematologic adverse events occurring in ≥10% pts were febrile neutropenia or other infection in 75%, hypophosphatemia in 22%, and hyperbilirubinemia in 10%. The 4-week and 8-week mortality rates were 9% and 25% in AML cohort and 0% and 13% in MDS/CMML cohort, respectively. Conclusion: AZA, VEN, and PEV combination is active and well-tolerated in both ND s-AML and MDS/CMML after HMA failure. This population was enriched with very poor risk features, including a majority of pts in the AML cohort with prior HMA or chemotherapy exposure for an antecedent myeloid malignancy and 1/3 of pts with a TP53 mutation. Response rates were high across disease subgroups, although duration of responses and survival were modest in pts with historically poor risk features, including those with adverse risk cytogenetics and TP53 mutations. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

Frameless Cobalt60-Based Hypofractionated Stereotactic Radiosurgery (HSRS) for Brain Metastases: Impact of Dose and Volume

<h3>Purpose/Objective(s)</h3> Frameless, gated, image-guided, Cobalt⁶⁰-based hypofractionated stereotactic radiosurgery (Co⁶⁰-HSRS) is a novel technical paradigm in the treatment of brain metastases that allows for both the dosimetric benefits of the Co⁶⁰ based stereotactic radiosurgery (SRS) platform as well as the biologic benefits of fractionation. We report mature local control (LC) and adverse radiation effects (ARE) outcomes following 5 fraction Co⁶⁰-HSRS for intact brain metastases. <h3>Materials/Methods</h3> All patients with intact brain metastases treated with 5-fraction Co⁶⁰-HSRS between 2017-2020 were retrospectively reviewed. Patients were typically selected for HSRS as opposed to single fraction SRS if the metastases were larger (>2cm diameter), were in eloquent areas, or were in proximity to another lesion receiving HSRS. Survival estimates were determined per patient using Kaplan Meier methods, and LC as well as symptomatic ARE rates were determined per lesion using competing risk methods. Univariable competing risk regression using Fine and Gray's methods were performed, and subsequent multivariable (MVA) regression using a backwards step-wise selection technique generated the final adjusted models. <h3>Results</h3> In total 299 metastases in 146 patients were identified. The median clinical and radiologic follow-up was 10.6 (range 0.5-49.9) and 10.7 months (range 0.5-47.6), respectively. The median maximum tumor diameter and volume were 1.7 cm (range, 0.2-3.9 cm) and 2.38 cc (range, 0.004-24.92 cc), respectively. The median total dose and prescription isodose was 27.5 Gy (range, 20-27.5 Gy) in 5 daily fractions and 52% (range, 45%-93%), respectively. The median overall survival (OS) was 12.7 months and the 1-year LC rate was 85%. MVA identified a total dose of 27.5 Gy vs. ≤25 Gy (hazard ratio [HR] 0.59, p = 0.042), and prior chemotherapy exposure (HR 1.99, p = 0.015), as significant predictors of LC. The 1-year ARE rate was 10.8% and the symptomatic ARE rate was 1.8%. MVA identified a gross tumor volume of ≥4.5cc (HR 7.29, p < 0.001) and a mean intra-tumoral dose of ≥39 Gy (HR 3.17, p = 0.034) as significant predictors of symptomatic ARE. <h3>Conclusion</h3> Moderate total doses in 5 daily fractions of Co⁶⁰-HSRS were associated with high rates of LC and a low incidence of symptomatic ARE. A prescription dose of 27.5 Gy was superior with respect to local control versus ≤25 Gy in 5 daily fractions. Target volumes of 4.5cc or larger as well as mean dose >39 Gy, were associated with higher rates of symptomatic necrosis. Further study will help refine the optimal dosimetric constraints for Co⁶⁰-HSRS.

Cost-Effectiveness of Pharmacologic Treatment Options for Women With Endocrine-Refractory or Triple-Negative Metastatic Breast Cancer.

Treatments for endocrine-refractory or triple-negative metastatic breast cancer (mBC) are modestly effective at prolonging life and improving quality of life but can be extremely expensive. Given these tradeoffs in quality of life and cost, the optimal choice of treatment sequencing is unclear. Cost-effectiveness analysis can explicitly quantify such tradeoffs, enabling more informed decision making. Our objective was to estimate the societal cost-effectiveness of different therapeutic alternatives in the first- to third-line sequences of single-agent chemotherapy regimens among patients with endocrine-refractory or triple-negative mBC. Using three dynamic microsimulation models of 10,000 patients each, three cohorts were simulated, based upon prior chemotherapy exposure: (1) unexposed to either taxane or anthracycline, (2) taxane- and anthracycline-exposed, and (3) taxane-exposed/anthracycline-naive. We focused on the following single-agent chemotherapy regimens as reasonable and commonly used options in the first three lines of therapy for each cohort, based upon feedback from oncologists treating endocrine-refractory or triple-negative mBC: (1) for taxane- and anthracycline-unexposed patients, paclitaxel, capecitabine (CAPE), or pegylated liposomal doxorubicin; (2) for taxane- and anthracycline-exposed patients, Eribulin, CAPE, or carboplatin; and (3) for taxane-exposed/anthracycline-naive patients, pegylated liposomal doxorubicin, CAPE, or Eribulin. In each cohort, accumulated quality-adjusted life-years were similar between regimens, but total societal costs varied considerably. Sequences beginning first-line treatment with paclitaxel, carboplatin, and CAPE, respectively, for cohorts 1, 2, and 3, had lower costs and similar or slightly better outcomes compared with alternative options. In this setting where multiple single-agent chemotherapy options are recommended by clinical guidelines and share similar survival and adverse event trajectories, treatment sequencing approaches that minimize costs early may improve the value of care.

Gamma knife icon based hypofractionated stereotactic radiosurgery (GKI-HSRS) for brain metastases: impact of dose and volume.

Gamma Knife Icon-based hypofractionated stereotactic radiosurgery (GKI-HSRS) is a novel technical paradigm in the treatment of brain metastases that allows for both the dosimetric benefits of the GKI stereotactic radiosurgery (SRS) platform as well as the biologic benefits of fractionation. We report mature local control and adverse radiation effect (ARE) outcomes following 5 fraction GKI-HSRS for intact brain metastases. Patients with intact brain metastases treated with 5-fraction GKI-HSRS were retrospectively reviewed. Survival, local control, and adverse radiation effect rates were determined. Univariable and multivariable regression (MVA) were performed on potential predictive factors. Two hundred and ninety-nine metastases in 146 patients were identified. The median clinical follow-up was 10.7months (range 0.5-47.6). The median total dose and prescription isodose was 27.5Gy (range, 20-27.5) in 5 daily fractions and 52% (range, 45-93), respectively. The median overall survival (OS) was 12.7months, and the 1-year local failure rate was 15.2%. MVA identified a total dose of 27.5Gy vs. ≤ 25Gy (hazard ratio [HR] 0.59, p = 0.042), and prior chemotherapy exposure (HR 1.99, p = 0.015), as significant predictors of LC. The 1-year ARE rate was 10.8% and the symptomatic ARE rate was 1.8%. MVA identified a gross tumor volume of ≥ 4.5cc (HR 7.29, p < 0.001) as a significant predictor of symptomatic ARE. Moderate total doses in 5 daily fractions of GKI-HSRS were associated with high rates of LC and a low incidence of symptomatic ARE.

Identifying BRCA wild-type ovarian cancers with a homologous recombination deficiency phenotype (101)

<b>Objectives:</b> It is unknown how best to evaluate <i>BRCA</i> wild-type ovarian carcinomas for homologous recombination deficiency (HRD), and previous studies did not show a survival advantage for <i>BRCA1</i> methylation. We sought to further characterize <i>BRCA1/RAD51C</i> promoter methylation in ovarian cancer (OC). We hypothesized that a combined assay with quantitative methylation and mutation assessment would identify <i>BRCA</i> wild-type ovarian carcinomas with an HRD phenotype. <b>Methods:</b> Digital droplet PCR primers and probes were designed to target CpG sites in the promoter regions of <i>BRCA1</i> and <i>RAD51C</i> known to be associated with transcriptional repression. Multiple aspects of the assay were tested and optimized in a CLIA environment. The fraction of methylated alleles was corrected for neoplastic cellularity and ≥60% was considered highly methylated. The methylated ddPCR (MddPCR) assay was then applied to DNA from banked epithelial ovarian cancer specimens previously assessed by methylation-sensitive PCR (MSP) and BROCA next-generation sequencing. RNA expression of a subset of <i>BRCA1</i> methylated samples was determined using RNA-seq, and expression was compared with methylation using LOESS regression. Clinical characteristics were then compared between highly methylated and unmethylated samples using a t-test for continuous variables, Fisher's exact test for categorical variables, and the log-rank test for overall survival (OS). Additional cases with germline/somatic mutations in homologous recombination repair (HRR) genes identified by BROCA sequencing were included in an overall survival analysis using the log-rank test. <b>Results:</b> Total 370 epithelial OC specimens were tested by MddPCR. MddPCR had 100% concordance with MSP. Among the samples, 9.5% were positive for <i>BRCA1</i> promoter methylation, and 3% were positive for <i>RAD51C</i> promoter methylation ≥5%. RNA expression analysis of a sub-set of <i>BRCA1</i> methylated samples demonstrated that the degree of <i>BRCA1</i> methylation was negatively correlated with <i>BRCA1</i> expression levels (r=-0.82, p<0.001). There were 26 highly methylated neoplastic <i>BRCA1</i> or <i>RAD51C</i> samples, 14 samples with low methylation (5-59% methylated alleles), and 294 samples with no methylation or HRR mutation. The median overall survival was 76 months for highly methylated cases compared to 50 months for unmethylated cases (HR: 0.66, p=0.20). Highly methylated samples were significantly less likely to have had prior chemotherapy exposure (12% vs 31%, <i>p</i>=0.04). Paired primary/recurrent samples were evaluated, two of which contained a highly methylated initial sample and showed a decrease in methylation at the time of recurrence. In the expanded cohort including HRR mutated OC, median OS was 80 months in cases with either high methylation or a non-<i>BRCA</i> HRR mutation compared to 50 months in unmethylated wild-type samples (HR: 0.63, p=0.02), with a survival curve similar to <i>BRCA</i> mutated samples (median OS: 66 months, HR: 0.76, p=0.01). <b>Conclusions:</b> Ovarian cancer that was either highly methylated or had a non-<i>BRCA</i> HRR mutation was associated with increased OS compared to unmethylated/wild-type cases, suggesting an HRD phenotype. Methylated samples had similar OS to HRR mutated cancers; however, survival analysis was limited by the low total number of highly methylated samples. Exposure to chemotherapy may decrease promoter methylation, and analysis of additional paired samples is ongoing. Quantitative methylation analysis could augment tumor sequencing in identifying OC with a favorable response to PARP inhibitors.Fig. 1

Five years survival outcomes of head and neck cancer patients treated with palliative metronomic chemotherapy.

e18009 Background: Palliative metronomic chemotherapy improved overall survival over intravenous chemotherapy in head and neck cancers. However, there is no data available about the 5-year outcomes with this regimen. Methods: This was a single-arm prospective study that enrolled head and neck squamous cell carcinoma patients warranting palliative chemotherapy. The chemotherapy administered was methotrexate 15 mg/m2 per oral weekly and celecoxib 200 mg per oral daily till the development of intolerable side effects or progression. Kaplan Meier method was used for estimation of OS and factors impacting the same were sought. A p-value of 0.05 was considered significant. Results: 200 patients were enrolled with a median age was 49.5 years (Range 22-85 years) and preponderance of male gender (175, 87.5%). The predominant site of malignancy was oral cavity in 144 patients (72.2%). Prior chemotherapy exposure was present in 78 patients (39%). The median FACT trial outcome index score was 43.7 (16.7-80.7). The median OS was 194 days (95%CI 181.7-206.3) . The 1-year, 3-years and 5-years OS were 17 %(Standard error-2.8%), 7.9% (Standard error-2.5%), and 3.9% (Standard error- 2%) respectively. The details of factors impacting OS are given in Table. Conclusions: Oral metronomic chemotherapy leads to a small proportion of patients having long term survival with metronomic chemotherapy. Clinical trial information: CTRI/2015/11/006392. [Table: see text]

Treatment (tx) patterns among men with metastatic castration resistant prostate cancer (mCRPC) in the United States (US).

52 Background: Novel hormonal therapies (NHTs) and docetaxel were initially approved for the tx of men with mCRPC. Over time, these agents moved earlier in the disease continuum and are now also used in metastatic castration sensitive prostate cancer (mCSPC). Little is known about first-line (1L) mCRPC tx patterns for men with prior taxane-based chemotherapy (CT) or NHT exposure. This study evaluated the impact of taxane CT or NHT use in mCSPC on recent 1L tx patterns among men with mCRPC in the US. Methods: Participating physicians collected information from medical charts for the next consecutive 4 adult men with mCRPC during January-August 2020. A subset of men had prior mCSPC tx information available. 1L mCRPC txs were described overall and stratified by previous tx with taxane CT or NHT during mCSPC. No statistical comparisons were performed. Results: 116 adult men with mCRPC and known mCSPC tx history were included. Mean age was 70 years; 15% had known family history of prostate cancer; 70% had bone metastases and 33% had visceral metastases at data collection. Overall, 10% (12/116) of men had been previously treated with taxane CT and 28% (32/116) were treated with NHT during mCSPC. 1L mCRPC tx was initiated on average 35 days after mCRPC diagnosis. NHT was the most common 1L mCRPC tx regardless of prior taxane CT or NHT use. Men pre-treated with taxane CT were more likely to initiate mCRPC tx with NHT than taxane naïve men. NHT pre-treated men were less likely to initiate 1L mCRPC tx with NHT and more likely to initiate tx with docetaxel than NHT naïve men. 53% of men with prior NHT tx were rechallenged with NHTs in 1L mCRPC. (Table). Conclusions: Findings from this US real-world study among men with mCRPC suggest physicians most commonly initiate 1L mCRPC life-prolonging tx with NHT regardless of prior taxane CT or NHT exposure. Additional studies with larger sample sizes are needed to confirm these findings and better understand optimal tx sequencing, especially as new tx options become available.[Table: see text]

Abstract P1-07-08: Endoxifen predicts early recurrence in breast cancer: A Brazilian prospective study

Abstract Tamoxifen is widely used in adjuvant therapy for breast cancer patients, but up to one-third of patients recur within 15 years after surgery even with its regular use. Low plasma levels of (Z)-endoxifen, the most active tamoxifen metabolite, have been studied as a possible predictor of treatment failure. Here, we evaluated plasma (Z)-endoxifen as a predictor of response to adjuvant treatment in breast cancer patients. Methods: One hundred forty nine patients were selected from a prospective cohort of consecutive newly diagnosed breast cancer patients recruited at a national referral center for treatment of cancer in Curitiba, Southern Brazil. Inclusion criteria were breast cancer women on stage I - III, positive hormone receptor tumors, operable, undergoing or not (neo)adjuvant chemotherapy, and signed for adjuvant tamoxifen for at least five years. At diagnosis, peripheral blood samples were collected for CYP2D6 genotyping for *1 *2, *3, *4, *5, *6, *7, *8, *9, *10, *17, *29 and *41 and subsequent metabolic activity scores according to phenotypes assigned for each allele (poor metabolizer PM; intermediate, IM; extensive, EM and ultrarapid metabolizer, UM). After the tamoxifen initiation, patients were evaluated at months 3, 6, and 12 for adherence and drug interactions, and plasma (Z)-endoxifen quantification. They were followed from April 2014 to April 2019. The study's primary objective was to evaluate whether (Z)-endoxifen plasma levels predict early recurrence in patients on adjuvant tamoxifen. The secondary aim was to evaluate an association between (Z)-endoxifen levels and clinical and phenotypic CYP2D6 metabolism variables. A Cox model estimated hazard ratios (HR) comparing recurrence free survival (RFS) according to (Z)-endoxifen plasma levels. The survival was compared using the Kaplan-Meier method and the log-rank test. Results: The median follow-up period was 52.3 months and at that point, there were 20 recurrences of 149 patients. At 3 months there were no cases of low adherence to tamoxifen. The (Z)-endoxifen levels were established by quartiles, with the first lower quartile being used as a cutoff (14.72nM). High (Z)-endoxifen levels at 3 months (&amp;gt;14.72nM) were detected in 75.8% (n = 113) of cases and low levels (≤14.72nM) in 24.2% (n = 36). There was no statistically significant difference between the groups with low or high (Z)-endoxifen levels regarding clinical and pathological variables, but there was a higher CYP2D6 PM/IM frequency in the low (Z)-endoxifen levels group (p&amp;lt;0.001). High (Z)-endoxifen levels were associated with lower RFS compared to low (Z)-endoxifen levels (HR 2.5, 95% CI 1.00-6.22, p=0.041). Low (Z)-endoxifen levels increased the recurrence risk even when adjusted for staging and molecular subtypes (HR 2.55, 95% CI 1.00-6.48, p&amp;lt;0.001) or staging and CYP2D6 phenotype (UM/EM vs IM/PM; HR 4.38, 95% CI 1.66-11.59, p=0.003), or prior chemotherapy exposure (HR 2.65, 95% CI 1.06-6.61, p=0.036). Conclusion: This is the first Brazilian prospective trial evaluating the association of plasma (Z)-endoxifen levels, with the clinical outcome in breast cancer women treated with adjuvant tamoxifen, controlled by predictable confounding factors of plasma (Z)-endoxifen levels, such as tamoxifen adherence, and drug interaction with CYP2D6 inhibitors. In our study, a low plasma level of (Z)-endoxifen (≤ 14.72nM) after 3 months of tamoxifen treatment was a predictor of early recurrence in patients under adjuvant tamoxifen (p=0.041). A longer follow-up and a larger cohort may be needed to confirm the (Z)-endoxifen cutoff value that is a predictor of long-term recurrence. Citation Format: Thais Almeida, Werner Schroth, Jeanine Marie Nardin, Thomas Mürdter, Solane Picolotto, Reiner Hoppe, Jenifer Primon Kogin, Elisa Daniele Gaio, Angela Dasenbrock, Raquel Cristina Skrsypcsak, Lucia Noronha, Hiltrud Brauch, José Claudio Casali-da-Rocha. Endoxifen predicts early recurrence in breast cancer: A Brazilian prospective study [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P1-07-08.