Mucocele-like lesions diagnosed on breast core biopsy: Assessment of upgrade rate and need for surgical excision

Mucocele-like lesion (MLL) is a rare mucinous lesion of the breast with highly variable upgrade rates to atypia or malignancy on excision. This spectrum of data has led to differing opinions on the need for surgical excision. We evaluated 50 core biopsy specimens diagnosed as having MLLs and correlated the findings with those of excision pathology. Thirty-eight patients underwent surgical excision and 29 were benign (76%), 4 had atypical ductal hyperplasia (11%), and 5 had ductal carcinoma in situ (13%), with an overall upgrade rate of 13%. However, the risk of upgrade was exclusively associated with the presence of atypia as seen on the needle core biopsy. All 22 MLLs without atypia had benign excisions, while 5 (31%) of the 16 patients with MLLs with atypia were upgraded to ductal carcinoma in situ on excision. No invasive carcinoma was identified. We believe it is reasonable that women with the core biopsy diagnosis of MLL without atypia and no associated mass be offered close clinical follow-up as an alternative to surgery.