Metastatic Colon Adenocarcinoma in a 15-Year-Old Teenager: A Case Report.

Colorectal cancer is predominantly an adult malignancy and is extremely rare in children. In pediatric patients, it is often associated with genetic predisposition syndromes such as Lynch syndrome or familial adenomatous polyposis. We report the case of a 15-year-old patient admitted for progressively worsening peri-umbilical abdominal pain. Thoraco-abdomino-pelvic computed tomography (CT) revealed parietal thickening of the right third of the transverse colon associated with deep lymphadenopathy and a focal lesion in segment III of the liver. The patient underwent a colonic biopsy, which revealed intramucosal colorectal adenocarcinoma. The clinical course was complicated by bowel obstruction requiring surgery, during which a diverting ileostomy, liver biopsy, and mesenteric lymph node resection were performed. Histopathological examination confirmed metastatic involvement from the primary colonic tumor. Immunohistochemical analysis demonstrated microsatellite instability (MSI) (loss of MLH1/PMS2). The patient subsequently received treatment with pembrolizumab.