Cytologic analysis of metaplastic breast carcinoma: Review of 66 cases diagnosed at the Institut Curie

Objectives Cytology reports of metaplastic breast carcinoma (MBC) are rare and limited to short series and simple case reports. To adapt cytology diagnostic criteria to the most recent fifth edition of the World Health Organization Classification of Breast Tumours from 2019, we have reviewed our series from the files of the Institut Curie.Methods A cohort of 66 female patients investigated by cytology with corresponding histologic diagnosis of MBC was identified. Eight cytologic characteristics were analyzed: cellularity, adenocarcinoma cells, squamous cells, spindle cells, giant cells, cytonuclear atypia, necrosis, and osseous/chondroid matrix and compared with histology.Results Cytologic diagnoses were malignant in 58 (88%) cases (of which 29 cases were typed cytologically as MBC), suspicious in 6 (9%) cases, and nondiagnostic in 2 (3%) cases. None of the cytologic examinations was a benign diagnosis. Low-grade adenosquamous carcinoma and fibromatosis-like metaplastic carcinoma exhibited a low degree of cellular atypia. Fibromatosis-like metaplastic carcinoma and spindle cell carcinoma (SpCC) presented spindle cells, while SpCC also demonstrated varying degrees of atypia, the presence of giant cells, and necrosis. Squamous cell carcinoma was characterized by the presence of squamous cells, and metaplastic carcinoma with osseous/chondroid differentiation displayed an osseous/chondroid matrix.Conclusions Fine-needle aspiration holds considerable potential as a valid, independent, and complementary approach to histologic examination of MBC.