Mixed Adenocarcinoma and Squamous Cell Carcinoma of Duodenum: A Case Report and Review of the Literature.

Despite being the largest part of the human gastrointestinal (GI) tract, the small intestine accounts for only 1-1.4% of all GI malignancies. Adenocarcinoma is the most common primary small bowel malignancy, with the most common site being the duodenum. On the other hand, squamous cell carcinoma (SCC) of the duodenum is extremely uncommon. We report the first case of mixed adenocarcinoma and SCC occurring in the third part of duodenum (D3). Our patient, a 64-year-old female with history of GERD, hypertension, and IDDM presented with 4 weeks of nausea, vomiting, and abdominal pain. Tomographic imaging of her abdomen demonstrated a distended stomach and a proximal duodenum with narrow caliber changes at the level of D3. An EGD revealed a tight stricture at D3 that could not be traversed. Stricture biopsies revealed duodenal mucosa with two small foci of SCC (positive for p63 and CK5/6) and adenocarcinoma (positive for CK7 and Moc31). Peritoneal metastases were detected on exploratory laparotomy, making the tumor surgically incurable. As she progressively declined and with worsening liver enzymes and general debility, she was not a candidate for chemotherapy and was eventually discharged on home hospice. Small bowel SCC/adenocarcinoma is an exceedingly uncommon cancer, making further case reports such as ours important to understand the nature of this entity and establish management guidelines.