Solid papillary carcinoma of the breast with an associated Cytokeratin 7- negative Paget's disease of the nipple. Report of a first case.

Solid papillary carcinoma (SPC) is a rare neoplasm of the breast showing a distinct morphology, neuroendocrine differentiation and should be divided into invasive and in situ subtype according to the current 2012 WHO classification of breast tumors. Here, we describe a case of a pure SPC, invasive-type, in a 31-years old female with an associated mammary Paget's disease (MPD) of the nipple showing a rare, CK7-negative immune phenotype, which has not been reported so far. This unusual differential diagnosis should be added to the rare condition of CK7-negative Paget's disease of the breast and complement a new feature to the characterization of SPC.