PRMT5 and neoplasm: PRMTs have recently received considerable attention as potential therapeutic targets in various types of cancer,31 and several specific PRMT inhibitors have recently been described.14 The present study suggests a promising therapeutic potential for PRMT5 targeting in a subset of TNBC, using the small‐molecule inhibitor EPZ015666.13, 14, 27 Indeed, we show that PRMT5 inhibition (a) impairs breast cancer cell viability, (b) triggers apoptosis, (c) impedes colony formation (d) affects CSC properties, and (e) slows tumor growth in a TNBC patient‐derived xenograft model (PDX).