Purpose or Case Report: Early onset colorectal cancer (EOCRC) in children has an incidence of approximately 1 per million, representing only 1% of all pediatric malignancies. Despite being rarer in the pediatric population, pediatric rectal carcinoma is on the rise and has worse outcomes than in adults. A large cohort study identified adenocarcinoma as the most common rectal tumor in pediatric patients and the major cause of death in this category of patients. Most EOCRC tumors are sporadic, with only 20-30% of patients having a hereditary genetic predisposition with Lynch syndrome being the most common hereditary cancer syndrome implicated in the pathogenesis of EOCRC. Pediatric rectal tumors tend to be larger and more likely to have lymph node involvement, and distant metastases.

The subject of this case is a 17-year-old female presenting with rectal bleeding and weight loss. She underwent a colonoscopy which was suggestive of proctitis and biospies were taken. The clinical presentation and scope exam were suggestive of inflammatory bowel disease such as ulcerative colitis. Magnetic resonance enterography (MRE) was ordered to check for small bowel disease involvement. MRE showed circumferential rectal wall thickening and enhancement with corresponding restricted diffusion, associated with multiple polypoid lesions protruding into the perirectal fat and some of which appears inseparable from the adjacent uterus. There were also multiple enlarged perirectal lymph nodes. The biopsies from the colonoscopy demonstrated non specific inflammatory changes. Based on the MRE findings which were suggestive of malignant process, a biopsy of one of the rectal polyps was performed and showed evidence of rectal adenocarcinoma. CT chest, abdomen and pelvis demonstrated metastatic lung nodules and liver lesion. Staging rectal MRI was also performed at an outside adult institution. Patient was then started on chemotherapy. Genetic testing identified a heterozygous germline variant of uncertain significance in the POLD1 gene. Germline POLD1 mutations were historically associated with polyposis of the GI tract and early onset colorectal cancer and there have been increasing reports of patients with mutations in this gene who did not have polyps prior to cancer development.

The aim of this case report is to underscore the importance of exploring this diagnosis when imaging findings do not align with a suspected benign condition.
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