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Case Reports

Abstract

Rare subtypes of extramammary Paget disease (EMPD) continue to present a diagnostic challenge. Goblet cell adenocarcinoma (GCA) is a rare intestinal neoplasm with hybrid epithelial and neuroendocrine features and an aggressive clinical course. GCA is most often found in the appendix and is exceptionally rare outside the tubular gut. We present a case of EMPD of the perianal skin associated with a subcutaneous mass in a 61-year-old man presenting with perianal rash. Histological analysis revealed invasive GCA in the subcutaneous soft tissue, accompanied by extensive secondary Paget disease involving the perianal skin and focally squamous epithelium of the anal canal. The tumor showed nests, tubules, and aggregates of goblet-like cells with intracytoplasmic mucin resembling colonic crypts, which were diffusely positive for CK20 and CDX2, expressed synaptophysin, chromogranin and INSM-1, and were negative for GATA-3, p40, and NKX3.1. The intraepidermal component showed focal CK7 positivity. These findings suggested likely metastatic spread from an underlying gastrointestinal adenocarcinoma, but there were no mucosal abnormalities by colonoscopy or evidence of metastatic disease by systemic imaging. Furthermore, an abdominoperineal resection and appendectomy confirmed no dysplasia or carcinoma involving any portion of the intestinal wall. This case therefore represents a unique occurrence of a primary extramucosal goblet cell adenocarcinoma likely originating from an anal fistula or an embryologic remnant and highlights the importance of considering unusual primary malignancies in the differential diagnosis of anogenital Paget disease. The clinical and treatment follow up and differential diagnosis of this very rare presentation of perianal EMPD are discussed.