Advanced mucinous adenocarcinoma of the ascending colon with duodenal invasion: a surgical and diagnostic challenge.

Mucinous adenocarcinoma (MAC) is a distinct subtype of colorectal cancer that is more often diagnosed at an advanced stage and has been associated with greater local invasiveness and a less favourable response to chemotherapy. We report a man in his 80s who presented with progressive weight loss, abdominal pain and altered bowel habits. Diagnostic evaluation revealed a large ascending colon mass extending to the hepatic flexure, with direct duodenal invasion causing high-grade obstruction. The patient underwent an en bloc extended right hemicolectomy with duodenal resection and reconstruction. Histopathological examination confirmed a moderately differentiated MAC, pathological stage pT4bN0. He subsequently received adjuvant capecitabine and remained under follow-up for approximately 3 years. This case highlights the aggressive nature of MAC and its uncommon but recognised extension into the duodenum.