Mucocele-like lesions in the breast diagnosed with percutaneous biopsy: is surgical excision necessary?

The purpose of this study was to determine the frequencies of atypia and cancer at excisional biopsy of lesions with a diagnosis of mucocele-like lesion (MLL) at percutaneous breast biopsy.

Retrospective review of 9286 lesions subjected to percutaneous imaging-guided biopsy identified MLLs in 35 (0.38%) patients. Medical records, imaging studies, and histologic results were reviewed.

Of the 35 patients with core biopsy findings of MLL, 27 underwent stereotactic core needle biopsy (19 with microcalcifications, five with calcifications with an associated mass, and three with only a mass), and eight underwent ultrasound-guided core needle biopsy (four with a solid mass, three with a complex cystic mass). At core biopsy, 12 of 35 (34%) MLLs were associated with atypia (10 cases of atypical ductal hyperplasia, two of flat epithelial atypia), and 23 of 35 (66%) were benign MLL only. All 12 MLLs associated with atypia and 12 of 23 benign MLLs were surgically excised. Eleven patients did not undergo surgery, five of whom were lost to follow-up. One of the 12 (3% of the 35) MLLs associated with atypia was upgraded to DCIS. None were upgraded to invasive cancer. None of the benign MLLs were upgraded to malignancy, and findings at excision of four of the 23 (17%) benign MLLs led to a change in diagnosis to a high-risk lesion (three atypical ductal hyperplasia, one atypical lobular hyperplasia).

MLL is a rare diagnosis but is encountered in large-volume breast practices. The findings are nonspecific with a range of imaging appearances. No imaging test is reliable for differentiating MLL from other suspicious lesions or lesions with associated atypia. Surgery is clearly warranted for MLL associated with atypia at core needle biopsy because it may be upgraded to malignancy upon excision. However, if the presence of atypia at excision of benign MLL will change clinical management, then benign MLL at core needle biopsy warrants surgical excision in some cases. In patients whose treatment will not change if atypia is found at excision, close surveillance with short-interval follow-up is a reasonable alternative.