Abstract
While the co-occurrence of breast cancers of different histological types within one breast is not uncommon, there are relatively few reports of distinct histological subtypes occurring simultaneously within the same tumor. Here, we report a case of mixed invasive ductal and lobular carcinomas in situ within a single tumor. An 81-year-old woman presented to our hospital with a spiculated mass in the right breast that had been detected by mammography. Further examination by breast ultrasonography revealed a mass measuring 10 mm in the right breast (area A). A core needle biopsy revealed invasive ductal carcinoma. The patient underwent right breast-conserving surgery along with sentinel lymph node biopsy, which led to the diagnosis of stage I breast cancer. Histopathological findings indicated coexisting invasive ductal and lobular carcinomas in situ within the same tumor. Notably, the ductal carcinoma exhibited positive staining for epithelial-cadherin, whereas the lobular carcinoma exhibited negative staining. This led to a final diagnosis of mixed breast carcinoma comprising both subtypes. Both subtypes were estrogen receptor-positive, progesterone receptor-positive, and human epidermal growth factor receptor 2-negative. The patient received postoperative radiation therapy and is currently undergoing treatment with aromatase inhibitors. Two years postoperatively, the patient is alive without recurrence.
