Juvenile colon cancer diagnosed by onset of intussusception: a case report suggestive of Lynch syndrome treated with laparoscopic colectomy

Abstract Background: One characteristic of Lynch syndrome, which is caused by germline mutations in a group of genes encoding mismatch repair proteins, is the early onset of colorectal cancer. Here, we report a rare case of juvenile colon cancer, diagnosed based on the onset of intussusception with high microsatellite instability (MSI) and the absence of BRAF mutations, which was suggestive of Lynch syndrome. Case presentation: A 28-year-oldman presented with right lower abdominal pain for approximately 3 months and defecated blacky stool for several weeks. He visited our hospital because of increasingly intense right lower abdominal pain. Computed tomography revealed a contrast-enhanced tumor and lymph nodes with a crab-claw-like fitted image extending into the ascending colon. Colon endoscopy revealed a large submucosal tumor-like lesion with ulceration. Laparoscopy-assisted ileal resection with level 3 lymph node dissection was performed 3 days after the endoscopic reduction of the intussusception. The histological diagnosis was a poorly differentiated adenocarcinoma. Gene analysis of the resected tumor revealed high MSIand KRAS mutations, and the absence of BRAF mutations. Immunohistochemistry indicated the absence of MLH1 and PMS2 expression in tumors. Genetic analysis of peripheral blood and tumors revealed no pathological mutations in MLH1, MSH2, PMS2, or MSH6. Conclusion A rare case of Lynch-like syndrome was diagnosed with intussusception. MSI-high, wild-type BRAF, and the absence of MLH1 and PMS2 expression suggested Lynch syndrome. The absence of pathological mutations in germline and somatic genes suggests the possibility of MLH1 promoter methylation or MLH1 epimutation in the pathogenesis of this case.