In 1986 mucocele-like lesions (MLL) were described as benign tumors; s
ubsequent reports identified MLL associated with ductal hyperplasia or
carcinoma (CA). To characterize MLL further, we studied 53 lesions fr
om 49 patients, in whom 25 MLL were benign and 28 were malignant (14 i
n situ, 14 invasive). Two had bilateral benign MLL, and two had bilate
ral MLL with CA. Patients ranged in age from 24 to 79 years (mean, 48
years). There were no appreciable differences in age, tumor size, or l
aterality between patients with benign or malignant MLL, although MLL
with CA had coarse calcifications more often than benign MLL and were
more likely to be detected mammographically. Intraductal carcinoma was
micropapillary or cribriform, and invasive carcinoma was usually muci
nous. Fewer of the benign lesions were estrogen and progesterone recep
tor positive. HER2/neu positivity was more common in MLL with CA. Know
n treatment was as follows: for benign MLL, excisional biopsy was done
in 22 patients (one with axillary dissection) and total mastectomy in
one patient; for MLL with CA, excisional biopsy was done in 17 patien
ts, biopsy followed by wider excision in four patients (three of whom
had axillary dissection), and mastectomy and axillary dissection in fi
ve patients (one also had radiotherapy). Follow-up ranged from less th
an a 1 year to 15 years (mean and median, 3.7 years). Two patients had
recurrences in the breast (one benign MLL and one MLL with CA). At th
e time of this report, all were alive without evidence of disease. We
conclude that MLL with CA is a low-grade neoplasm with few clinical di
fferences from benign MLL except for more prominent calcifications, le
ading to mammographic detection. Excisional biopsy is recommended for
benign MLL. Breast-conserving surgery is appropriate therapy for MLL w
ith CA. Radiotherapy is indicated if CA involves margins or if extensi
ve intraductal carcinoma is present.