The coexistence of lobular carcinoma in a fibroadenoma with a malignant phyllodes tumor in the opposite breast: report of a case.

It is very unusual for a carcinoma of the breast to coexist with a phyllodes tumor, or for a carcinoma to arise within a fibroadenoma. We present herein an extremely rare case of lobular carcinoma in situ arising in a fibroadenoma, associated with a malignant phyllodes tumor in the opposite breast. A 49-year-old woman was admitted to our hospital with a large mass in the right breast and a small mass in the left breast. Microscopic examination of biopsy materials revealed a malignant phyllodes tumor in the right breast and a fibroadenoma in the left breast, for which a right standard radical mastectomy and left lumpectomy were performed. Microscopic findings of the material excised from the left breast showed the presence of multiple lobular carcinoma in situ within the tumor mass of the fibroadenoma. However, histological examination did not detect any metastasis to the bilateral axillary lymph nodes. To our knowledge this is the only such case ever to be reported in Japan.