Case reports of malignant mucocele-like lesions.

Mucocele-like lesions (MLL) of the breast have been reported as extremely rare as well as benign, but now it is believed they can be both malignant and benign. This paper describes two cases of malignant MLL, both subjected to immunohistochemical staining. Case 1: A 42-year-old woman with multiple malignant MLLs without evidence of a mass at presentation to our hospital after biopsy, but whose ultrasonogram showed small multiple hypoechoic lesions. Case 2: A 70-year-old woman, whose left breast cancer was found on routine mammography after modified radical mastectomy for right breast cancer. Pathologically, MLL with intraductal carcinoma was diagnosed. Case 1 underwent two lumpectomies in 3 years, but even now new lesions have developed. However, the patient refused to have another operation. C-erbB2 was negative in both cases. When malignant MLL is histologically of low grade, excisional biopsy is sufficient for a single MLL with intraductal carcinoma, while it may be necessary to perform a subcutaneous mastectomy for multiple lesions.