Infiltrating micropapillary carcinoma of the breast. Cytologic findings

OBJECTIVE: To examine the cytologic features of infiltrating micropapillary carcinoma (IMPC). METHODS: Using the histopathology files of one of the authors (I.J.B.), we retrospectively identified 20 IMPC cases (pure, 12; partial micropapillary carcinoma differentiation, 8) with corresponding cytology. We evaluated the cases for cellularity, atypia, architecture and background. RESULTS: All cases were diagnostic of malignancy, characterized by atypical cells present predominantly in three-dimensional clusters and single cells, facilitating the diagnosis. The clusters had cell ball and papillarylike arrangements, like the morular growth pattern seen on histopathology. Apocrine cytology was present in 12 cases, focal mucin background in 5 and psamomma bodies in 2. The differential diagnosis includes primary papillary neoplasms of the breast, metastatic ovarian papillary serous carcinoma, apocrine and colloid carcinoma of the breast, and intraductal carcinoma (micropapillary type). CONCLUSION: As in histopathology, the cytologic features of IMPC are unique and should be recognized due to its aggressive behavior.