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.