Phase Ib study of pembrolizumab in combination with trastuzumab emtansine for metastatic HER2-positive breast cancer.

BACKGROUND: Preclinical and clinical data support potential synergy between anti-HER2 therapy plus immune checkpoint blockade. The safety and tolerability of trastuzumab emtansine (T-DM1) combined with pembrolizumab is unknown. METHODS: This was a single-arm phase Ib trial (registration date January 26, 2017) of T-DM1 plus pembrolizumab in metastatic, human epidermal growth factor receptor 2 (HER2)-positive breast cancer. Eligible patients had HER2-positive, metastatic breast cancer previously treated with taxane, trastuzumab, and pertuzumab, and were T-DM1-naïve. A dose de-escalation design was used, with a dose-finding cohort followed by an expansion cohort at the recommended phase 2 dose (RP2D), with mandatory baseline biopsies. The primary endpoint was safety and tolerability. Secondary endpoints included objective response rate (ORR) and progression-free survival (PFS). Immune biomarkers were assessed using histology, protein/RNA expression, and whole exome sequencing. Associations between immune biomarkers and treatment response, and biomarker changes before and during treatment, were explored. RESULTS: 20 patients received protocol therapy. There were no dose-limiting toxicities. The RP2D was 3.6 mg/kg T-DM1 every 21 days plus 200 mg pembrolizumab every 21 days. 85% of patients experienced treatment-related adverse events (AEs) ≥grade 2, 20% of patients experienced grade 3 AEs, and no patients experienced grade >4 AEs. Four patients (20%) experienced pneumonitis (three grade 2 events; one grade 3 event). ORR was 20% (95% CI 5.7% to 43.7%), and median PFS was 9.6 months (95% CI 2.8 to 16.0 months). Programmed cell death ligand-1 and tumor infiltrating lymphocytes did not correlate with response in this small cohort. CONCLUSIONS: T-DM1 plus pembrolizumab was a safe and tolerable regimen. Ongoing trials will define if there is a role for checkpoint inhibition in the management of HER2-positive metastatic breast cancer. TRIAL REGISTRATION NUMBER: NCT03032107.

Clinical Efficacy and Whole-Exome Sequencing of Liquid Biopsies in a Phase IB/II Study of Bazedoxifene and Palbociclib in Advanced Hormone Receptor-Positive Breast Cancer.

PURPOSE: Sensitivity to endocrine therapy (ET) is critical for the clinical benefit from the combination of palbociclib plus ET in hormone receptor-positive/HER2-negative (HR+/HER2-) advanced breast cancer. Bazedoxifene is a third-generation selective estrogen receptor (ER) modulator and selective ER degrader with activity in preclinical models of endocrine-resistant breast cancer, including models harboring ESR1 mutations. Clinical trials in healthy women showed that bazedoxifene is well tolerated. PATIENTS AND METHODS: We conducted a phase Ib/II study of bazedoxifene plus palbociclib in patients with HR+/HER2- advanced breast cancer who progressed on prior ET (N = 36; NCT02448771). RESULTS: The study met its primary endpoint, with a clinical benefit rate of 33.3%, and the safety profile was consistent with what has previously been seen with palbociclib monotherapy. The median progression-free survival (PFS) was 3.6 months [95% confidence interval (CI), 2.0-7.2]. An activating PIK3CA mutation at baseline was associated with a shorter PFS (HR = 4.4; 95% CI, 1.5-13; P = 0.0026), but activating ESR1 mutations did not impact the PFS. Longitudinal plasma circulating tumor DNA whole-exome sequencing (WES; N = 68 plasma samples) provided an overview of the tumor heterogeneity and the subclonal genetic evolution, and identified actionable mutations acquired during treatment. CONCLUSIONS: The combination of palbociclib and bazedoxifene has clinical efficacy and an acceptable safety profile in a heavily pretreated patient population with advanced HR+/HER2- breast cancer. These results merit continued investigation of bazedoxifene in breast cancer.

Molecular correlates of response to eribulin and pembrolizumab in hormone receptor-positive metastatic breast cancer.

Immune checkpoint inhibitors (ICIs) have minimal therapeutic effect in hormone receptor-positive (HR+ ) breast cancer. We present final overall survival (OS) results (n = 88) from a randomized phase 2 trial of eribulin ± pembrolizumab for patients with metastatic HR+ breast cancer, computationally dissect genomic and/or transcriptomic data from pre-treatment tumors (n = 52) for molecular associations with efficacy, and identify cytokine changes differentiating response and ICI-related toxicity (n = 58). Despite no improvement in OS with combination therapy (hazard ratio 0.95, 95% CI 0.59-1.55, p = 0.84), immune infiltration and antigen presentation distinguished responding tumors, while tumor heterogeneity and estrogen signaling independently associated with resistance. Moreover, patients with ICI-related toxicity had lower levels of immunoregulatory cytokines. Broadly, we establish a framework for ICI response in HR+ breast cancer that warrants diagnostic and therapeutic validation. ClinicalTrials.gov Registration: NCT03051659.

Clinical Efficacy and Molecular Response Correlates of the WEE1 Inhibitor Adavosertib Combined with Cisplatin in Patients with Metastatic Triple-Negative Breast Cancer.

PURPOSE: We report results from a phase II study assessing the efficacy of the WEE1 inhibitor adavosertib with cisplatin in metastatic triple-negative breast cancer (mTNBC). PATIENTS AND METHODS: Patients with mTNBC treated with 0-1 prior lines of chemotherapy received cisplatin 75 mg/m2 i.v. followed 21 days later by cisplatin plus adavosertib 200 mg oral twice daily for five doses every 21 days. The study had 90% power to detect the difference between null (20%) and alternative (40%) objective response rates (ORR) with a one-sided type I error of 0.1: an ORR >30% was predefined as making the regimen worthy of further study. RNA sequencing and multiplex cyclic immunofluorescence on pre- and post-adavosertib tumor biopsies, as well as targeted next-generation sequencing on archival tissue, were correlated with clinical benefit, defined as stable disease ≥6 months or complete or partial response. RESULTS: A total of 34 patients initiated protocol therapy; median age was 56 years, 2 patients (6%) had BRCA2 mutations, and 14 (41%) had one prior chemotherapy. ORR was 26% [95% confidence interval (CI), 13-44], and median progression-free survival was 4.9 months (95% CI, 2.3-5.7). Treatment-related grade 3-5 adverse events occurred in 53% of patients, most commonly diarrhea in 21%. One death occurred because of sepsis, possibly related to study therapy. Tumors from patients with clinical benefit demonstrated enriched immune gene expression and T-cell infiltration. CONCLUSIONS: Among patients with mTNBC treated with 0-1 prior lines, adavosertib combined with cisplatin missed the prespecified ORR cutoff of >30%. The finding of immune-infiltrated tumors in patients with clinical benefit warrants validation.