The significance of extracellular mucin in breast fine needle aspiration specimens

To determine if all breast fine needle aspiration (FNA) specimens with abundant extracellular mucin require excisional biopsy.

Fifty cases of breast FNA containing extracellular mucin, reported with a recommendation for biopsy and with histological follow-up were reviewed. Cellular features were noted, and the cases reclassified ignoring the presence of mucin and then correlated with histological outcome.

Subsequent histology showed benign changes in 20% (10/50), two cases (4%) of atypical ductal hyperplasia (ADH) and 76% (38/50) to be malignant lesions, including three cases of ductal carcinoma in situ (DCIS). When the FNA cases were reviewed disregarding the presence of mucin, 11 cases were reclassified as benign and one case that contained mucin-like material but no epithelial cells reviewed as non-diagnostic. All cases of invasive mixed and mucinous carcinoma (MC) would have been reported with a recommendation for histological examination. In addition, the three cases each of fibroadenoma (FA) and a benign mucocoele-like lesion (MLL) were correctly identified as benign. However, two cases each of DCIS and ADH would have been reported benign with no recommendation for further histology.

Breast FNA specimens with mucinous material may arise from sampling of a range of benign and malignant processes; however, a biopsy should be recommended, even in cases of low cellularity, owing to sampling problems and the frequent co-occurrence of significant lesions. FNA is highly accurate at predicting carcinoma with mucinous differentiation although it is not possible to reliably predict if the lesion represents pure MC or a mixed carcinoma.