Metaplastic breast cancer is heterogeneous; treatment should be personalized

Abstract

Background: Metaplastic breast cancers are uncommon, predominantly triple-negative with generally poor outcomes and consist of various combinations and permutations of squamous carcinoma and sarcomatous components. Aims: To learn from our population of metaplastic carcinomas the relevance of predictive biomarkers. Methods: The anatomic pathology database was searched for metaplastic carcinoma. H&E and IHC slides were reviewed and clinical information gleaned from the HIS. Results & Conclusions: There were 2,804 breast cancer diagnosis and 1,720 HER2 tests in a 5-year period. Six patients were diagnosed with metaplastic carcinoma. Two patients had squamous carcinoma (pure, which is HER2-overexpressed/ER-/PR-, 1 case; and PR-weak/ER-/HER2-negative, with residual invasive breast carcinoma, no special type [IBCNST]). One had triple-negative spindle cell sarcoma with residual ER-weak IBCNST. The rest have heterologous sarcoma (ER-negative osteosarcoma, 1 case; triple negative chondrosarcoma with squamous carcinoma or IBCNST, 2 cases). The single patient with a huge HER2-overexpressed squamous metaplastic carcinoma (pT3N2)showed partial pathological response to neoadjuvant Herceptin therapy and went on to survive with disease for at least 4 years. We conclude that metaplastic carcinoma is rare in our population, is heterogeneous in composition and expression of predictive markers, and are mostly high-grade in histology, but have meaningful survival if targeted therapy can be offered.