Additional mimics of mucinous mammary carcinoma: fibroepithelial lesions

To determine the origin and nature of mucinlike material in fine-needle aspiration (FNA) smears of the breast in noncancerous breast lesions, we studied breast FNA smears from four patients. All smears contained epithelial cells floating in a mucinlike background, which raised suspicion for mucinous (colloid) carcinoma. Mucicarmine stain was performed on one smear from each case. Subsequent tissue biopsy specimens were studied using mucicarmine, periodic acid-Schiff with and without diastase, and alcian blue stains at pH 2.7 and 0.9 on selected tissue sections. Correlation of the cytologic and histologic findings of each lesion was performed. The mucinlike background in all four FNA smears stained strongly with mucicarmine. Corresponding biopsy specimens revealed pseudoangiomatous hyperplasia in the first case, fibroadenoma and atypical ductal hyperplasia in the second, benign phyllodes tumor in the third, and fibroadenoma in the fourth. Each lesion in cases 1 to 3 was associated closely with fibrocystic changes. In case 4, cystic changes were located within the fibroadenoma. On tissue sections of all four cases, the cyst contents and 10% to 50% of normal lobule and duct contents stained with mucicarmine, indicating that the cyst contents were the most probable source of mucin in the FNA smears. The presence of pools of mucicarmine-positive material in FNA smears of the breast is not an exclusive feature of mucinous carcinoma; mucicarmine-positive mucin can arise from benign cystic changes as well as from normal lobules and ducts.