Biopsy of the duodenum confirmed a poorly differentiated carcinoma with AE1/AE3 (+), CK7 (+), CK19 (−), CK8/18 (+), hepatocytes (−), epithelial membrane antigen (EMA) (+), TTF‐1 (−), and Ki‐67 (approximately 60%+) (Fig 4b), indicative of sarcomatoid carcinoma. The gene discussed is MUC1; the disease is sarcomatoid carcinoma.