Depressed-type submucosal invasive colorectal cancer in a patient with Lynch syndrome diagnosed using short-interval colonoscopy.

Although regular colonoscopy surveillance is recommended for patients with Lynch syndrome (LS) who underwent partial colectomy, the appropriate interval has not been determined. We report a case of colorectal cancer (CRC) detected by short-interval surveillance colonoscopy (SC) in a patient with LS having a past history of partial colectomy. A 65-year-old man underwent sigmoidectomy for advanced CRC. His family history revealed that his two younger brothers had CRC in their twenties and thirties, respectively, and the patient met with the criteria in the Revised Bethesda Guidelines. After confirming the loss of MSH2 protein expression in the primary tumor, subsequent genetic testing showed germline mutation with a large deletion of exon 7-14 in the MSH2 gene, indicating a diagnosis of LS. After the diagnosis of LS, the patient underwent annual SC. Three years after the initial surgery, superficial submucosal invasive cancer was detected. Subsequently, SC after a 6-month interval revealed a deep submucosal invasive cancer (7 mm in diameter). Although additional surgery was recommended, considering his comorbidities, regular SC rather than colectomy was selected. Even shorter-interval SC carried out within a year is not sufficient to detect endoscopically resectable tumors in some high-risk LS cases.