Fibromatosislike metaplastic carcinoma of the breast as a diagnostic pitfall for fine needle aspiration cytology: a case report

BACKGROUND Metaplastic carcinomas of the breast are uncommon, and most display marked cellular atypia. Recently, a low grade fibromatosis-like metaplastic carcinoma was found and displayed little nuclear atypia. CASE A 74-year-old woman presented with a 2.5-cm, palpable breast nodule. Mammogram was reported as suspicious for malignancy. Cytologic examination revealed smears of low cellularity with most cells lying in clusters and having a round or oval shape. Rare cells had a "spindle" shape. Nuclear features were low grade. Rare individual cells had retained cytoplasm. Lumpectomy revealed a fibromatosis-like metaplastic carcinoma. CONCLUSION: Cytologically, fibromatosis-like metaplastic carcinomas are low grade lesions producing smears of relatively low cellularity. Separation from ductal carcinomas is necessary because fibromatosis-like metaplastic carcinomas rarely metastasize to lymph nodes.