Florid, papillary endosalpingiosis of the axillary lymph nodes.

A 55-year-old woman underwent radical mastectomy and axillary node dissection because of an invasive ductal carcinoma with neuroendocrine features. Histologically, all 22 sampled lymph nodes had widespread cystic inclusions lined by a regular, serous-type epithelium positive for cytokeratin-7, WT-1, CA125, and estrogen receptors. Papillary projections were found in the lumen of some cysts. The lesions were consistent with florid, papillary endosalpingiosis (FPE), a hitherto unreported condition in a supradiaphragmatic location. Metastases from papillary carcinomas of ovary, breast, or thyroid were excluded considering the lesion's immunophenotype (negative for mammaglobin and TTF-1) and the absence of both atypical features and a concurrent abdominal serous tumor. In only one node, lesions co-existed with a metastasis of breast carcinoma. Supradiaphragmatic FPE represents a pitfall in the differential diagnosis of metastases, especially in sentinel nodes, since it may increase their size and reveal an unusual ultrasonographic image. Clinicopathologic findings and a focused immunohistochemical study led to the correct diagnosis of this benign lesion.