[A Case of Serrated Polyposis Syndrome with Early Colon Cancer].

The patient was a 65-year-old man without any noteworthy medical history. A colonoscopy conducted after a positive fecal occult blood test revealed approximately 100 polyps in the large intestine. A biopsy of some these polyps revealed serrated and hyperplastic polyps, which were histologically determined to be well-differentiated adenocarcinoma. Based on these findings, a diagnosis of serrated polyposis syndrome (SPS) was made, and the patient underwent laparoscopic pancolectomy/ileoproctostomy. Histopathological analysis revealed a total of 91 lesions, out of which 15 were ≥10 mm. A 30 mm lesion in the ascending colon was a well-differentiated adenocarcinoma, stage Ⅰ colon cancer (T1a [sm], ly0, v0, N0, and M0). No germline mutations were found on genetic testing of the adenomatous polyposis coli (APC), mutY homolog (MUTYH), mutL homolog 1 (MLH1), mutS homolog 2 (MSH2), mutS homolog 6 (MSH6), and postmeiotic segregation increased 2 (PMS2) genes. No loss of MLH1 protein expression or expression of mutated B-Raf (BRAF) V600E protein was observed in the cancer regions after immunostaining. This case is important because not only is the condition rare but also because it showed that the serrated pathway may not necessarily be the mechanism by which serrated lesions become cancerous in patients with SPS.