Fine needle aspiration cytologic findings of breast mucinous neoplasms: differential diagnosis between mucocelelike tumor and mucinous carcinoma

OBJECTIVE: To report the cytologic findings of mucocelelike tumor and mucinous carcinoma. STUDY DESIGN: All mucinous neoplasms diagnosed by fine needle aspiration and confirmed by histologic examination were reviewed to detect the cytologic findings helpful for the differentiation. The cytologic findings were correlated with the histologic findings. RESULTS: Cytologically, mucinous carcinomas were highly cellular and showed many single epithelial cells and variably formed epithelial cell clusters in abundant extracellular mucin. Malignant cells exhibited round, atypical nuclei; granular chromatin; and small nucleoli. Mucocele like tumor showed low cellularity with scanty, monolayered, small sheets of epithelial cells and abundant, extracellular mucin. Myoepithelial cells were present within the epithelial cell sheets. Tumor cells were usually small, with uniform, round nuclei; fine chromatin; and absence of nucleoli. CONCLUSION: Cytologic findings of mucocelelike tumor and mucinous carcinoma were different in cellularity, shape of cell clusters and nuclear features, although mucocelelike tumors having a carcinoma component were similar to mucinous carcinoma. Awareness of the cytologic findings of breast mucinous neoplasms is important to make a specific diagnosis.