Duodenal cancer is a cancer in the first section of the small intestine known as the duodenum. Cancer of the duodenum is relatively rare compared to stomach cancer and colorectal cancer. Its histology is usually adenocarcinoma. Familial adenomatous polyposis (FAP), Gardner syndrome, Lynch syndrome, Muir¨CTorre syndrome, celiac disease, Peutz¨CJeghers syndrome, Crohn's disease and juvenile polyposis syndrome are risk factors for developing this cancer. The duodenum is the first part of the small intestine. It is located between the stomach and the jejunum. After foods combine with stomach acid, they descend into the duodenum where they mix with bile from the gallbladder and digestive fluid from the pancreas.

Reference
Wiki: Duodenal cancer