A case of colon cancer implanted on endoscopic resection ulcer certified by cancer genomic testing.

A 90 year-old man underwent endoscopic mucosal resection for lesions in the descending and sigmoid colons as well as endoscopic submucosal dissection (ESD) for a lesion in the rectal peritoneal reflection (Ra) 1 month before undergoing laparoscopic resection and D3 dissection for advanced cancer in the descending colon. One year later, he underwent a surveillance colonoscopy, and advanced colorectal cancer was detected on the ESD scar. The history suggested that this newly detected recurrent colorectal neoplasm on the ESD scar may have originated from cancer cells derived from the descending colon cancer that were implanted in the ESD ulcer, thereby initiating a new colorectal neoplasm. Cancer genomic testing further indicated that three of the four pathogenic variants detected in the recurrent colorectal neoplasm were consistent with pathogenic variants of descending colon cancer. This finding strongly supports our contention that cancer cells derived from the descending colon cancer were implanted in the post-ESD ulcer of the rectal Ra and proliferated, forming the recurrent colorectal neoplasm. This case report highlights the potential for tumor cell implantation on endoscopic resection ulcers and the utility of cancer genomic testing in validating this phenomenon.