Multiple pilomatrixomas in a survivor of WNT‐activated medulloblastoma leading to the discovery of a germline APC mutation and the diagnosis of familial adenomatous polyposis

Because children diagnosed with WNT‐activated medulloblastoma have a 10‐year overall survival rate of 95%, active long‐term follow‐up is critically important in reducing mortality from other causes. Here, we describe an 11‐year‐old adopted female who developed multiple pilomatrixomas 3 years after diagnosis of WNT‐activated medulloblastoma, an unusual finding that prompted deeper clinical investigation. A heterozygous germline APC gene mutation was discovered, consistent with familial adenomatous polyposis. Screening endoscopy revealed numerous precancerous polyps that were excised. This case highlights the importance of long‐term follow‐up of pediatric cancer survivors, including attention to unexpected symptoms, which might unveil an underlying cancer predisposition syndrome.