Fine-needle aspiration cytology of mucocelelike tumors of the breast.

Mucocelelike tumors of the breast encompass a spectrum of pathologic lesions, including benign tumor, atypical ductal hyperplasia, carcinoma in situ, and colloid carcinoma. Because the fine-needle aspiration (FNA) cytology of mucocelelike tumors covering this pathologic spectrum is not well defined, a study of 21 cases of mucocelelike tumors was conducted. Benign lesions are likely to be poorly cellular and to contain cohesive clusters of cytologically bland cells arranged in two dimensional sheets in the background of abundant mucoid material. Colloid carcinomas are usually highly cellular and contain loosely cohesive clusters and dissociated cells with nuclei showing minimal to mild atypia. The most discriminating feature between benign and malignant lesions appears to be the presence of many dissociated cells with intact cytoplasm. Cases with atypical ductal hyperplasia, with some bordering on carcinoma in situ as seen in 7 of the 12 benign cases, may be difficult to identify on FNA cytology, possibly because of sampling. As expected, some of the atypical cases have intermediate features of benign and malignant tumors. Because of overlapping features in borderline cases, we recommend excisional biopsy for all mucocelelike lesions. Myxoid fibroadenoma is more cellular than benign mucocelelike lesions and can be distinguished from carcinoma by the absence of dissociation and presence of numerous bare nuclei of bland morphology in the background. The mucoid material of myxoid fibroadenoma stained brightly pink rather than magenta as in mucocelelike tumors using the Diff Quik stain.