Metaplastic breast carcinoma: a rare breast cancer with distinct biology and therapeutic challenges

Metaplastic breast carcinoma (MpBC) is a rare, histologically heterogeneous breast cancer typically treated with regimens developed for triple-negative breast cancer (TNBC), despite distinct biology and insufficient response to standard therapy. MpBC is defined by differentiation of malignant epithelial cells toward non-glandular lineages, reflecting a plasticity that complicates biomarker interpretation and distinguishes it from non-metaplastic TNBC. In this review, we cover MpBC histopathology, biology, and therapeutic development, calling for dedicated clinical investigation that recognizes MpBC as a biologically distinct entity.