Mucocele-like lesions of the breast: A benign cause for indeterminate or suspicious mammographic microcalcifications

Most earlier reports of mucocele-like lesions (MILL) of the breast have dealt with symptomatic cases in premenopausal women or lesions found incidentally in breast biopsies performed for other reasons. The diagnosis of this lesion has special challenges in the setting of mammographic screening for breast cancer because the imaging characteristics of MILL may mimic those of ductal carcinoma in situ (DCIS), while mucinous carcinoma enters the differential diagnosis on cytologic grounds. This report focuses on our experience with MILLS detected during screening mammography. Cases with MLL as the final histologic diagnosis in our database during January 1992-June 2000 are included. The results of clinical, imaging, cytologic, core biopsy, and histologic examination of these lesions are recorded. The relevant literature is reviewed. Twenty-six cases were found, with a mean patient age of 57.5 years. Microcalcifications were the dominant radiologic abnormality in 22 cases (84.6%). Imaging was considered suspicious or almost certainly malignant in 17 cases (65.4%). Cytology was classified as atypical or suspicious in 17 cases (70.9%). However, open biopsy showed mostly benign changes, including atypical ductal hyperplasia (ADH) in five cases (19.2%). In one case, ADH merged with a 3-4 mm focus of low-grade DCIS. This, the largest series focusing purely on screen-detected MLL, suggests that the combination of clinical, imaging, and cytologic features of screen-detected MLL are different from those of mucinous carcinoma, symptomatic MLL, or incidental MLL. Correlating the cytomorphology of mucinous lesions of the breast with their mammographic appearance may permit more precise preoperative diagnosis.