Invasive Solid Papillary Carcinoma of the Nipple With Pagetoid Extension and Nodal Metastasis

We report a case of invasive solid papillary carcinoma (SPC) of the nipple with Pagetoid extension to the skin and lymph node metastasis. SPC is an uncommon primary breast cancer accounting for less than 1% of all breast cancers. Only 2 cases occurring in the nipple have been reported. However, both cases were without Pagetoid extension or lymph node metastasis. The presently reported tumor consisted of irregularly shaped solid cell nests with delicate fibrovascular cores. The tumor cells had round nuclei with low-grade atypia and eosinophilic cytoplasm. Neuroendocrine differentiation was confirmed by immunohistochemical positivity for CD56, synaptophysin, and chromogranin A. Immunohistochemistry also confirmed the absence of myoepithelial cells around the tumor cell nests. Therefore, a diagnosis of invasive SPC was made. Additionally, tumor cell deposits in the intramammary and axillary lymph nodes were identified, and these deposits had the same histological characteristics as the invasive SPC of the nipple. The invasiveness of SPC can be difficult to determine. However, the tumor cell nests in the current case exhibited a retraction artifact, which is known to be associated with invasive carcinoma and a poor prognosis, as well as morphological patterns that have been previously identified as characteristic of invasive SPC. Although SPC is widely recognized as having a favorable outcome, the existence of exceptionally aggressive cases occurring in the nipple must be recognized. Additional cases of invasive SPC of the nipple are needed to analyze the clinicopathological correlation.