Comparative cytology of mucocelelike lesion and mucinous carcinoma of the breast in fine needle aspiration

OBJECTIVE: To study the fine needle aspiration cytology (FNAC)features of m ucocelelike lesion (MLL) of the breast and to compare them to those of muci nous carcinoma. STUDY DESIGN: The fine needle aspiration (FNA) smears of 7 cases of histolo gically proven MLL (2 malignant and 5 benign, including 4 associated with a typical ductal hyperplasia) were reviewed and compared to those of 14 mucin ous carcinoma cases. RESULTS: In all cases, grossly visible thick, mucoid material was obtained from FNA. The most important features for distinguishing benign MLL from mu cinous carcinoma were: (2) scant cellularity; (2) no or rare single, intact tumor cells; (3) tumor cells arranged in cohesive monolayers; and (4) abse nce of significant nuclear atypia. In contrast, mucinous carcinoma in gener al showed higher cellularity; abundant single, intact cells; three-dimensio nal cellular clusters in most cases; and nuclear atypia ranging from mild t o severe. CONCLUSION: Mucinous lesions of the breast should be divided into MLL and f rank mucinous carcinoma based on FNAC. However, FNAC diagnosis of malignant MLL has yet to be defined. Excisional biopsy is advised for all hypocellul ar cases for further separation into benign and malignant MLL and to rule o ut the possibility of hypocellular mucinous carcinoma.