Background: Breast mucocele-like lesions (MLLs) are rare breast lesions. There is a paucity of literature on the rate of pathologic upstaging of MLL to in situ or invasive breast cancer. We sought to review our experience with MLL at a tertiary care center and review published literature. Methods: A retrospective review was undertaken of all patients with breast MLL at the Mayo Clinic, Rochester, from 1998 to 2016. Descriptive statistics were performed. Results: Overall, 30 patients were diagnosed with MLL, with a mean age of 54.6 years (range 51–58). Calcifications on screening mammogram were the most common method of MLL detection (n = 26, 86.7 %), with core needle biopsy (CNB) being performed in 29/30 patients. MLL with atypia was identified in 14 patients (48 %), and surgical excision was performed in 26 patients. Disease was upstaged to invasive disease in one patient (3.8 %) who presented with a palpable mass. With a median duration of follow up of 3.5 years [interquartile range 1–7.1], two patients developed contralateral invasive breast cancer (both patients had a remote history of invasive breast cancer on that side), and one patient developed contralateral in situ disease. Review of the literature demonstrates a 2.9 % upgrade rate of MLL without atypia on excisional biopsy. Conclusions: The upstage rate of MLL identified on CNB to invasive disease at surgical excision in this series was 3.8 %. In cases with MLL presenting as calcifications, no cases were upstaged in this series. Across the literature, upstage rates of MLL without atypia on CNB are low, indicating excisional biopsy may be avoided in these cases.
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