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.