Anal squamous cell carcinoma with metastasis to duodenum causing duodenal stricture and gastric outlet obstruction

Squamous cell carcinoma (SCC) of the anal canal is a rare entity encompassing only 2–4 percent of all colon, rectal, and anal cancers. SCC of the anal canal tends to be loco-regional, and in the event of distant metastasis, a most common site of spread is to liver and lung. We report an unusual case of SCC of the anal canal with duodenal metastases in a 49-year-old female who had presented with symptoms of abdominal pain, nausea, and vomiting eight months after the primary diagnosis of SCC of the anal canal. Esophagogastroduodenoscopy (EGD) revealed duodenal stricture with subsequent biopsy revealing duodenal mucosa with scattered malignant cell clusters within lymphatic spaces, consistent with metastatic carcinoma. Immunohistological staining demonstrated malignant cells positive for CK7, p16, p63 favoring a metastatic SCC.