Immunotherapy in Pediatric Constitutional Mismatch Repair Deficiency (CMMRD)-Associated Colorectal Cancer: Report of...

Constitutional mismatch repair deficiency is a rare pediatric cancer predisposition syndrome caused by mutations in mismatch repair genes.

We present the case of a 10-year-old with family history of Lynch syndrome, diagnosed with hepatic flexure adenocarcinoma and duodenal adenoma. Germline testing revealed a novel pair of biallelic PMS2 mutations. She received neoadjuvant ipilimumab and nivolumab, followed by total abdominal colectomy and adjuvant CAPEOX (capecitabine, oxaliplatin). Pathology revealed stage IIIB adenocarcinoma with partial response to immunotherapy.

This case highlights the use of immunotherapy and screening for pediatric CMMRD-associated colorectal adenocarcinoma in the setting of a novel PMS2 variant.