Composite encapsulated papillary carcinoma and solid papillary carcinoma

Encapsulated papillary carcinoma (EPC) and solid papillary carcinoma (SPC) are distinctive variants of intraductal papillary carcinomas, each accounting for <1% of breast carcinomas. Here we report a composite carcinoma consisting of EPC and SPC. A 73‐year‐old woman was found to have a high density mass in the left breast on mammogram. A biopsy showed intermediate to high grade ductal carcinoma in situ (DCIS). Gross examination of the lumpectomy specimen revealed a solid, multinodular mass. Microscopic examination demonstrated two morphologically distinct intraductal carcinomas intermingled with each other. One had delicate papillae in multi‐cystic spaces surrounded by thick fibrous capsule, consistent with EPC. The other had solid tumor nests with delicate fibrovascular cores. The cells were monotonous with round nuclei and salt and pepper‐like chromatin, characteristic of SPC. The lack of myoepithelial cells within the papillae and at the periphery of the lesion was confirmed by immunostaining for p63 and CK5/6. Neuroendocrine differentiation of SPC was demonstrated by neuron specific enolase staining. To our knowledge, this is the first reported case of composite EPC and SPC. It raises an interesting question as to a possible common pathway of carcinogenesis of these two rare variants.