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PURPOSE: Preclinical data demonstrating androgen receptor (AR)-positive (AR+) TNBC cells are sensitive to AR antagonists and PI3K inhibition catalyzed an investigator-initiated, multi-institutional phase Ib/II study TBCRC032. The trial investigated the safety and efficacy of the AR-antagonist enzalutamide alone or in combination with the PI3K inhibitor taselisib in patients with metastatic AR+ (≥10%) breast cancer. PATIENTS AND METHODS: Phase Ib patients (ER+ or TNBC) with AR+ breast cancer received 160 mg enzalutamide in combination with taselisib to determine dose-limiting toxicities and the maximum tolerated dose (MTD). Phase II TNBC patients were randomized to receive either enzalutamide alone or in combination with 4 mg taselisib until disease progression. Primary endpoint was clinical benefit rate (CBR) at 16 weeks. RESULTS: The combination was tolerated and the MTD was not reached. The adverse events were hyperglycemia and skin rash. Overall, CBR for evaluable patients receiving the combination was 35.7%, and median progression-free survival (PFS) was 3.4 months. Luminal AR (LAR) TNBC subtype patients trended towards better response compared to non-LAR (75.0% vs. 12.5%, p=0.06), and increased PFS (4.6 vs. 2.0 months, p=0.082). Genomic analyses revealed subtype-specific treatment response; and novel FGFR2 fusions and AR splice variants. CONCLUSIONS: The combination of enzalutamide and taselisib increased CBR in TNBC patients with AR+ tumors. Correlative analyses suggest AR protein expression alone is insufficient for identifying patients with AR-dependent tumors and knowledge of tumor LAR subtype and AR-splice variants may identify patients more or less likely to benefit from AR-antagonists. TRIAL REGISTRATION: ClinicalTrial.gov, Identifier: NCT02457910. Registered on May 29, 2015.

Purpose: Because of inherent disease heterogeneity, targeted therapies have eluded triple-negative breast cancer (TNBC), and biomarkers predictive of treatment response have not yet been identified. This study was designed to determine whether the mTOR inhibitor everolimus with cisplatin and paclitaxel would provide synergistic antitumor effects in TNBC.Methods: Patients with stage II/III TNBC were enrolled in a randomized phase II trial of preoperative weekly cisplatin, paclitaxel and daily everolimus or placebo for 12 weeks, until definitive surgery. Tumor specimens were obtained at baseline, cycle 1, and surgery. Primary endpoint was pathologic complete response (pCR); secondary endpoints included clinical responses, breast conservation rate, safety, and discovery of molecular features associated with outcome.Results: Between 2009 and 2013, 145 patients were accrued; 36% of patients in the everolimus arm and 49% of patients in the placebo arm achieved pCR; in each arm, 50% of patients achieved complete responses by imaging. Higher rates of neutropenia, mucositis, and transaminase elevation were seen with everolimus. Clinical response to therapy and long-term outcome correlated with increased frequency of DNA damage response (DDR) gene mutations, Basal-like1 and Mesenchymal TNBC-subtypes, AR-negative status, and high Ki67, but not with tumor-infiltrating lymphocytes.Conclusions: The paclitaxel/cisplatin combination was well tolerated and active, but addition of everolimus was associated with more adverse events without improvement in pCR or clinical response. However, discoveries made from correlative studies could lead to predictive TNBC biomarkers that may impact clinical decision-making and provide new avenues for mechanistic exploration that could lead to clinical utility. Clin Cancer Res; 23(15); 4035–45. ©2017 AACR.

Purpose: Metastatic breast cancers continue to elude current therapeutic strategies, including those utilizing PI3K inhibitors. Given the prominent role of PI3Kα,β in tumor growth and PI3Kγ,δ in immune cell function, we sought to determine whether PI3K inhibition altered antitumor immunity.Experimental Design: The effect of PI3K inhibition on tumor growth, metastasis, and antitumor immune response was characterized in mouse models utilizing orthotopic implants of 4T1 or PyMT mammary tumors into syngeneic or PI3Kγ-null mice, and patient-derived breast cancer xenografts in humanized mice. Tumor-infiltrating leukocytes were characterized by IHC and FACS analysis in BKM120 (30 mg/kg, every day) or vehicle-treated mice and PI3Kγnull versus PI3KγWT mice. On the basis of the finding that PI3K inhibition resulted in a more inflammatory tumor leukocyte infiltrate, the therapeutic efficacy of BKM120 (30 mg/kg, every day) and anti-PD1 (100 μg, twice weekly) was evaluated in PyMT tumor–bearing mice.Results: Our findings show that PI3K activity facilitates tumor growth and surprisingly restrains tumor immune surveillance. These activities could be partially suppressed by BKM120 or by genetic deletion of PI3Kγ in the host. The antitumor effect of PI3Kγ loss in host, but not tumor, was partially reversed by CD8+ T-cell depletion. Treatment with therapeutic doses of both BKM120 and antibody to PD-1 resulted in consistent inhibition of tumor growth compared with either agent alone.Conclusions: PI3K inhibition slows tumor growth, enhances antitumor immunity, and heightens susceptibility to immune checkpoint inhibitors. We propose that combining PI3K inhibition with anti-PD1 may be a viable therapeutic approach for triple-negative breast cancer. Clin Cancer Res; 23(13); 3371–84. ©2016 AACR.

Purpose: Tumor-infiltrating lymphocytes (TIL) in the residual disease (RD) of triple-negative breast cancers (TNBC) after neoadjuvant chemotherapy (NAC) are associated with improved survival, but insight into tumor cell-autonomous molecular pathways affecting these features are lacking. Experimental Design: We analyzed TILs in the RD of clinically and molecularly characterized TNBCs after NAC and explored therapeutic strategies targeting combinations of MEK inhibitors with PD-1/PD-L1–targeted immunotherapy in mouse models of breast cancer. Results: Presence of TILs in the RD was significantly associated with improved prognosis. Genetic or transcriptomic alterations in Ras–MAPK signaling were significantly correlated with lower TILs. MEK inhibition upregulated cell surface MHC expression and PD-L1 in TNBC cells both in vivo and in vitro. Moreover, combined MEK and PD-L1/PD-1 inhibition enhanced antitumor immune responses in mouse models of breast cancer. Conclusions: These data suggest the possibility that Ras–MAPK pathway activation promotes immune-evasion in TNBC, and support clinical trials combining MEK- and PD-L1–targeted therapies. Furthermore, Ras/MAPK activation and MHC expression may be predictive biomarkers of response to immune checkpoint inhibitors. Clin Cancer Res; 22(6); 1499–509. ©2015 AACR.