Surgical excision is warranted following a core biopsy diagnosis of mucocoele-like lesion of the breast.

AIMS: Mucocoele-like lesions (MLLs) of the breast are unusual lesions in which mucin-filled ducts or cysts are accompanied by extrusion of mucin into surrounding stroma. A possible diagnosis of MLL may be suggested by the finding of mucin-filled ducts or cysts and/or stromal mucin in a core biopsy sample. Whether such findings should prompt immediate open diagnostic biopsy to exclude malignancy is currently uncertain, although this represents current practice in our institution. In this study we have reviewed 11 cases of possible MLL on core biopsy correlating both pathological and radiological findings in order to determine the risks of associated malignancy and whether excision is the most appropriate management option.

METHODS AND RESULTS: Eleven cases of possible MLL presenting via the Breast Screening and Assessment Unit in Leeds since April 1999 were identified by review of pathological records. Histological slides, mammograms and ultrasound images were reviewed. Ten of the 11 had undergone open surgical biopsy for diagnosis. Three of the 10 (30%) proved to derive from malignant lesions. Two were ductal carcinoma in situ (DCIS) and one was an invasive mucinous carcinoma. All three cases had an associated atypical epithelial proliferation which, in a surgical excision, would be classified as atypical ductal hyperplasia (ADH) at least, as well as mucin in the core biopsy sample. The majority of possible MLLs presented radiologically as coarse calcification, but two of four (50%) which had a radiological mass subsequently proved malignant. Seven cases were without atypia on the core and all subsequently proved benign. Three of these, however, were associated with ADH on the excision biopsy.

CONCLUSION: Surgical excision is warranted following a core biopsy suggestion of possible MLL when mucin-filled ducts or cysts and stromal mucin have been seen. The risk of malignancy is high when the core biopsy also contains an atypical epithelial proliferation (100% in our series) and also when there is an associated radiological mass lesion. In cases without atypia on the core a significant proportion of cases (43%) are associated with ADH on excision.