Perez, Edith A.

11051 Background: A serious complication associated with breast cancer treatment is the increased risk for development of therapy-related acute myeloid leukemia (t-AML). To evaluate and possibly identify patients (pts) at high risk for development of t-AML, the Southwest Oncology Group asked whether dose-intensive adjuvant regimens for high risk breast cancer pts induced genetic damage to hematopoietic stem cells (HSC), defined by the emergence of clonal hematopoiesis, an early marker of HSC damage. Methods: 274 pts consented to the clonal hematopoiesis study objective of S0012, a randomized clinical trial of standard doxorubicin and cyclophosphamide followed by weekly paclitaxel (arm 1, 129 pts) vs. weekly doxorubicin and daily oral cyclophosphamide plus G-CSF followed by weekly paclitaxel (arm 2, 145 pts) as neoadjuvant therapy for inflammatory and locally advanced breast cancer. Two different clonality assays were used: the HUMARA (HUMan Androgen Receptor) Assay to estimate the incidence of early genetic damage by clonal proliferation and microsatellite instability (MSI) testing at 5 loci (Bat 26, Bat 40, APC, Mfd, D2S123), common ‘hotspots‘ in t-AML, to screen for loss of heterozygosity or defective DNA mismatch repair mechanisms. Blood samples were evaluated prior to treatment and at 6 and 12 mos post-surgery for emergence of clonal hematopoiesis. Results: Of the 274 pts enrolled, follow-up clonal hematopoiesis samples were available for 195 pts; 96 pts on arm 1 and 99 pts on arm 2. Both HUMARA and MSI results were negative for clonal hematopoiesis in 96% of samples analyzed. In 14 cases, the HUMARA assay suggested that a clonal population was present, but MSI analysis was negative. No cases were HUMARA+/MSI+. With a median follow-up of 19.6 mos, only one pt has developed t-AML 3 yr 5 mos post randomization. Her clonal hematopoiesis test samples at 6 and 12 mos following treatment were negative. Conclusions: Clonal hematopoiesis assays performed within the first year following neoadjuvant therapy and surgery on S0012 failed to identify an emerging clonal HSC population. Longer clinical follow-up will be necessary to define the positive predictive value of detecting clonal hematopoiesis in the 14 HUMARA+/MSI- cases as a harbinger of t-AML. No significant financial relationships to disclose.

603 Background: Breast MRI may be useful for detecting mammographically occult ipsilateral carcinoma in newly diagnosed breast cancer. Our initial experience with breast MRI, demonstrated 16% of patients to have additional breast disease detected only by preoperative MRI. We further analyzed our findings to identify an association between patient factors and MRI detected disease. Methods: Preoperative MRI scans of 390 women with newly diagnosed breast cancer were reviewed. Using only patients with pathologic verification, the incidence of mammographically occult ipsilateral cancer was determined. Patient and tumor characteristics were further analyzed to identify factors which may predict pathologically positive MRI findings. Results: Of the 390 women undergoing preoperative MRI, 120 (31%) had ipsilateral findings requiring biopsy. Pathologically verified additional ipsilateral cancer was detected in 62 (16%). Multicentric disease was detected in 32 (52%) and multifocal or more extensive local disease in 30 (48%). The median age of all patients was 62 (27% premenopausal) whereas the median age of those with MRI detected additional carcinoma was 55 (44% premenopausal). Of those with additional disease detected by MRI, 74% had index lesions =1 cm and 63% node negative. The most common histology of the index lesion was infiltrating ductal carcinoma in 64%. In the 62 patients found to have additional disease by MRI the most common histology included infiltrating ductal carcinoma (58%), ductal carcinoma-in-situ (34%) and infiltrating lobular (8%). The histology of the MRI detected additional disease was identical to the index lesion in 71%. Conclusions: In women with newly diagnosed breast cancer, there was a 16% incidence of pathologically proven, mammographically occult ipsilateral disease detected by MRI. Patients found to have additional disease tended to be younger, premenopausal or have index tumors =1cm. The contribution of preoperative MRI in breast cancer management continues to evolve. A lower threshold for obtaining breast MRI may be appropriate in selected subsets of breast cancer patients. No significant financial relationships to disclose.

579 Background: N9831 and other clinical trials have demonstrated the additive survival benefit of trastuzumab (H) therapy with chemotherapy for patients with resected HER-2 positive breast cancer. Cardiac toxicity (CTox) is increased by this strategy. Prediction of or early detection of CTox is important. Methods: 95 patients provided informed consent. Brain natriuretic peptide (BNP), C-reactive protein (CRP), troponin T (TnT) and I (TnI), TNF-alpha, IL-1b, and IL-6 were to be drawn at baseline, after initiation of doxorubicin/cyclophosphamide (AC), after initiation of paclitaxel (T), and after the initiation of H (may have been given concurrently with T). 67 patients with at least a baseline sample, a post-treatment sample, and a baseline and subsequent evaluation of LVEF were studied. No patient in this group had a grade 3 decline in LVEF. Only 3 of these patients did not receive H. Values above the 99th percentile were considered abnormal for troponin. 40 ng/ml was considered elevated for BNP. Results: Values of CRP, TNF-alpha, IL- 6 and IL1b changed in very few patients and without a discernible pattern. For further evaluation of BNP, TnI, and TnT, 2 definitions of CTox were tested: 1. a >10% drop in LVEF from baseline (n=27) and 2. a drop in LVEF of 10–15% to less than the institutional lower limit of normal (LLN) OR a >15% decline in LVEF (n=14). No pre-treatment marker appeared to predict a > 10% decline in LVEF (definition 1). For patients fulfilling definition 2, pre-treatment BNP > 40 was seen in 21% of patients vs 8% of normals (nls) (p= 0.18) and an abnormal TnI (>0.04) was seen in 21% vs 6% of nls (p=0.10). Only doubling of BNP appeared promising as a serial marker of CTox using definition 2 (27% vs 7% for nls (p = 0.09). Conclusions: Baseline BNP and TnI and serial measures of BNP may be promising for further investigation for the prediction and detection of treatment-related CTox. Due to limitations of the study including the small numbers of patients analyzed, the difficulty in defining CTox, and the variation in the timing of sample procurement and assessment, these data are considered exploratory. Supported by CA-25224, CA-2115, CA 38926, CA31946. No significant financial relationships to disclose.

78 Background: Previous study demonstrated that activation of RAS/MAPK pathway is associated with reduced tumor infiltrating lymphocytes and poor response to neoadjuvant chemotherapy in triple negative breast cancer (TNBC). Further study showed that inhibition of MAPK pathway with a MEK inhibitor is synergistic with anti-PD1/PD-L1 therapies. Methods: Patients with unresectable locally advanced or metastatic TNBC with ≤ 3 prior lines of therapy without prior anti-PD-1/PD-L1/PD-L2 therapies were enrolled. Treatment was started with a 2-week run in period with single agent binimetinib. Dose level 0 was binimetinib at 45 mg oral twice daily continuously and dose level -1 was 30 mg twice daily. Pembrolizumab was given at a fixed dose of 200 mg every 3 weeks at both dose levels. Phase I study was based on the standard 3+3 design. Results: A total of 12 patients were enrolled and treated in the phase 1. Five patients were enrolled at dose level 0, 1 patient withdrew prior to treatment and 1 patient was not evaluable for dose limiting toxicity (DLT). Among 3 evaluable patients, 2 patients experienced DLT with grade 3 flank pain and ALT abnormality. Additional 8 patients were enrolled at dose level -1. Out of 6 evaluable patients for DLT, there was 1 DLT observed with grade 3 AST and ALT abnormality. However, this particular patient had liver metastasis with grade 1 AST and ALT abnormality at baseline and her liver function test (LFT) normalized in 3 weeks after treatment discontinuation and oral prednisone. Other grade 1-2 common AEs included rash, LFT increase, abdominal pain, mucositis, nausea, cardiac troponin T increase without EKG change. The efficacy data will be presented at the meeting after the phase II interim analysis. Conclusions: Pembrolizumab in combination with binimetinib at 30 mg twice daily appears to be safe based on the initial cohort. Phase II part is currently ongoing with binimetinib 30 mg twice daily and pembrolizumab 200 mg every 3 weeks with a total of 23 patients planned where the safety and efficacy of this combination will be further evaluated. Clinical trial information: NCT03106415.

Abstract Purpose: Young age has been shown to be an independent predictor of poor outcome in breast cancer. In HER2-positive breast cancer, the effects of aging remain largely unknown. Experimental Design: A total of 4,547 patients were included [3,132 from North Central Cancer Treatment Group (NCCTG) N9831 and 1,415 from National Surgical Adjuvant Breast and Bowel Project (NSABP) B-31]. Pathologic stromal tumor-infiltrating lymphocyte (sTIL) and molecular tumor infiltrating lymphocyte (mTIL) signatures were evaluated. Results: In NCCTG N9831, comparable benefit of trastuzumab was observed in all patients [age ≤ 40; HR, 0.43; 95% confidence interval (CI), 0.28–0.66; P < 0.001; and age > 40; HR, 0.56; 95% CI, 0.45–0.69; P < 0.001]. Similar results were observed in NSABP B-31 (age ≤ 40; HR, 0.45; 95% CI, 0.29–0.68; P < 0.001; and age > 40; HR, 0.42; 95% CI, 0.33–0.54; P < 0.001). Among patients who received chemotherapy alone, younger age was associated with poor outcome in the hormone receptor–positive subset, but not the hormone receptor–negative subset, in both trials. Although there was no association between sTILs and age, a small, but significant increase in mTIL CD45 and some immune subset signatures were observed. Among patients who received chemotherapy alone, patients over 40 years of age with lymphocyte-predominant breast cancer had excellent outcome, with 95% remaining recurrence free at 15 years. Conclusions: Among patients treated with trastuzumab, there was no significant difference in outcome related to age. Our study suggests that trastuzumab can negate the poor prognosis associated with young age.

530 Background: Therapeutic efficacy of H involves activation of the immune system.Age-dependent progressive deterioration of the immune response is referred as immunosenescence. In HER2+ breast cancer, the effects of aging and the ability of H to activate endogenous anti-tumor immunity is unknown. A previous report from HERA trial showed no significant increase in risk of early recurrence with age (≤ or > 40). We evaluated the long-term outcome of HER2+ patients (pt) related to age and immune landscape. Methods: 1,392 pt from N9831 trial were evaluated. Stromal tumor infiltrating lymphocytes (sTIL) were evaluated in H&E slides. Lymphocyte predominant breast cancer (LPBC) was defined as sTIL ≥ 50%. Molecular TIL (mTIL) and immune subset signatures were evaluated using NanoString research CodeSets. Cox proportional hazard ratio (HR) was used for analysis. Results: There were 1,111 (79.8%) pt > 40 years old (yo) and 281 (20.2%) pt ≤ 40 yo. Younger age was significantly associated with hormone receptor positivity (p 0.00011) and luminal B subtype (p 0.011). With a median follow up of 10.6 years, there was no significant difference in long-term outcome among pt ≤ 40 vs. > 40 yo who received H (HR = 0.88 (0.62-1.24), p = 0.45). Similar findings were observed when age was dichotomized at 50 and 60 yo. While there was no association between sTIL and age, a small but significant increase in mTIL CD45 expression with age (p 0.003) was observed. Similar small increases in cytotoxic cell (p 0.007) and T cell (p 0.015) immune scores were also observed with increasing age. Among pt who received chemotherapy alone, pt > 40 yo with LPBC (n 55) had excellent outcome with 92.4% recurrence free survival (RFS) at 10 years. However, there was no significant difference in RFS among pt ≤ 40 yo with or without LPBC. Conclusions: Among pt treated with H, there was no significant difference in outcome related to age. In contrast to a decline expected from immunosenescence, we observed small but significant increases in mTIL signatures for total lymphocytes, cytotoxic, and T cell subsets. Among patients who received chemotherapy alone, our data suggested that pt > 40 yo with LPBC had excellent prognosis, compared to pt > 40 yo without LPBC.

Background: An expanded understanding of the biology of breast cancer has led to the identification of the HER-2 receptor as an important growth factor. This receptor possesses intrinsic tyrosine kinase activity and has been associated with aggressive biological behavior and poor clinical outcome. Methods: Data have been reviewed regarding the role of HER-2 expression as a prognostic variable, as a predictive factor for response to chemotherapy and hormonal therapies, and as a directed therapeutic target for breast cancer. Results: Therapy with a humanized monoclonal antibody to HER-2 (trastuzumab) can be effective treatment in some patients with metastatic breast cancer, either given alone or in combination with some chemotherapeutic agents. Cardiac toxicity limits concurrent use with anthracyclines. Clinical trials will further define optimal combination regimens with this agent, and its value in patients with localized or locally advanced stages. Conclusions: Trastuzumab is a significant addition to the armamentarium against breast cancer. Standardization of the optimal method to evaluate for HER-2 overexpression is necessary to better define its role as a prognostic, predictor, and therapeutic target in this disease.