Mucocele-like lesions of the breast: a clinical outcome and histologic analysis of 102 cases.

Mucocele-like lesions (MLLs) of the breast are characterized by cystic architecture with stromal mucin and frequent atypia, but it is unknown whether they convey long-term breast cancer risk. We evaluated 102 MLLs that were derived from a single-institution benign breast disease cohort of 13412 women who underwent biopsy from 1967 to 2001. MLLs were histologically characterized by type of lining epithelium, architecture of the lesion, associated atypical hyperplasia (AH), and incidence of breast cancer (14.8-year median follow-up). A relatively large proportion of MLLs (42%) were diagnosed in women older than 55 years. AH was significantly more frequent in MLL patient compared to the cohort overall (27% versus 5%; P < .001). Breast cancer has developed in 13 patients with MLL. This frequency is only slightly higher than population expected rates overall (standardized incidence ratio, 2.28; 95% confidence interval, 1.21-3.91) and not significantly different from women in the cohort with (nonatypical) proliferative breast lesions. Younger women (<45) with MLL had a nonsignificant increase in risk of cancer compared to the general population (standardized incidence ratio, 5.16; 95% confidence interval, 1.41-13.23). We conclude that MLL is an uncommon breast lesion that is often associated with coexisting AH. However, in women older than 45 years, MLLs do not convey additional risk of breast cancer beyond that associated with the presence of proliferative disease.