Mucocele-like lesion of the breast (MLL) is an uncommon entity, and recent studies show low rates of upgrade from core needle biopsy (CNB) to excision.


To evaluate features associated with upgrade of MLLs diagnosed on CNB.


Seventy-eight MLLs diagnosed on CNB from 1998–2019 and subsequent excisions were reviewed. Histologic parameters evaluated included the presence of atypia, presence and morphology of calcifications, and morphologic variant (classic [C-MLL], duct ectasia–like [DEL-MLL], or cystic mastopathy–like [CML-MLL]).


Overall, 45 MLLs lacked atypia and 33 were associated with atypia (atypical ductal hyperplasia, 32; atypical lobular hyperplasia, 1). Most were C-MLLs (61) with fewer DEL-MLLs (14) and CML-MLLs (3). Half showed both coarse and fine calcifications, with fewer showing only coarse or fine calcifications, and some showing none. Subsequent excision or clinical follow-up was available for 25 MLLs without atypia—of which 2 (8.0%) were upgraded to ductal carcinoma in situ (DCIS)—and 23 with atypia, of which 4 (17.4%) were upgraded to DCIS. No cases were upgraded to invasive carcinoma. All upgraded cases showed coarse calcifications on CNB, and all upgraded cases were associated with residual calcifications on post-CNB imaging.


Most MLLs present as calcifications and nearly half are associated with atypia. Upgrade to DCIS is twice as frequent in MLLs with atypia versus those without. A predominance of coarse calcifications and the presence of residual targeted calcifications following core biopsy may be associated with higher upgrade rates.

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Author notes

The authors have no relevant financial interest in the products or companies described in this article.

The findings were presented (in abstract form) at the 108th Annual Meeting of the United States and Canadian Academy of Pathology; March 16–21, 2019; National Harbor, Maryland.