A Case Series of Metastatic Metaplastic Breast Carcinoma Treated With Anti-PD-1 Therapy.

Metaplastic breast cancer is a rare and often chemo-refractory subtype of breast cancer with poor prognosis and limited treatment options. Recent studies have reported overexpression of programmed death ligand 1 (PD-L1) in metaplastic breast cancers, and there are several reports of anti-PD-1/L1 being potentially active in this disease. In this case series, we present 5 patients with metastatic metaplastic breast cancer treated with anti-PD-1-based therapy at a single center, with 3 of 5 cases demonstrating a response to therapy, and one of the responding cases being a metaplastic lobular carcinoma with low-level hormone receptor expression. Cases were evaluated for PD-L1 expression, tumor infiltrating lymphocytes (TILs), DNA mutations, RNA sequencing, and T-cell receptor sequencing. Duration of the response in these cases was limited, in contrast to the more durable responses noted in other recently published reports.
Competing Interests: WR: Research support from Galectin Therapeutics, Bristol Myers Squibb (BMS), Merck, Tesaro/GlaxoSmithKline, MiNA Therapeutics, Inhibrx, Veana Therapeutics, Aeglea Biotherapeutics, Shimadzu, OncoSec, and Calibr. Patents/Royalties: Galectin Therapeutics. Advisory Boards: Nektar Therapeutics, Vesselon. DP: Received advisory board honoraria and institutional research funding support from Brooklyn ImmunoTherapeutics, Bristol-Myers Squibb, and Merck Laboratories. DP receives speaker bureau honoraria from Genentech and Novartis. Unrelated to this work, DP has received additional advisory board honoraria from other entities. RB: Consulting fees: Genomic Health, Astra Zeneca, Genentech; Institutional research funding: Seattle Genetics, Ichnos Biosciences, Merck; Honoraria for speakers bureau: Genentech, Seattle Genetics. HM: Consulting or Advisory Role - AstraZeneca; Bristol-Myers Squibb; Daiichi Sankyo; Genentech; Genomic Health; Immunomedics; Lilly; Merck; Pfizer; Puma Biotechnology; Puma Biotechnology; Seattle Genetics, Research Funding - Bristol-Myers Squibb (Inst); Lilly (Inst); Merck, (Inst); ZIOPHARM Oncology (Inst), Travel, Accommodations, Expenses - Amgen; AstraZeneca; Bristol-Myers Squibb; DAVA Pharmaceuticals; Genentech; Immunomedics; Lilly; Merck; Pfizer; Puma Biotechnology; Spectrum Pharmaceuticals, Other Relationship - Genomic Health; Lilly. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
(Copyright © 2021 Kim, Rajamanickam, Bernard, Chun, Wu, Martel, Sun, Redmond, Sanchez, Basho, McArthur and Page.)