What happened, in summary

A 65-year-old man was diagnosed in 2016 with adenocarcinoma in the gastric antrum. He started neoadjuvant chemotherapy, but treatment was stopped after two cycles because of side effects. He then underwent subtotal gastrectomy with radical lymph-node dissection. The resected cancer was poorly differentiated and had clear margins.

About 20 months after gastric surgery, he developed rectal pain and tenesmus. Imaging showed abnormal thickening in the rectum, but the first biopsy found only inflammation. Because symptoms persisted, a defunctioning colostomy was created and he later underwent an ultra-low Hartmann's procedure. Surgery revealed peritoneal nodules and an advanced fibrotic rectal lesion.

Pathology confirmed that the rectal and pericolonic tumor was metastatic gastric adenocarcinoma rather than a new colorectal cancer. He later had repeated admissions for small-bowel obstruction and was not well enough for further chemotherapy. He died six months after the rectal operation.