MB-73: CASE REPORT: MULTIPLE PILOMATRIXOMAS IN A SURVIVOR OF WNT+ MEDULLOBLASTOMA LEADING TO THE DISCOVERY OF A GERMLINE APC MUTATION AND THE DIAGNOSIS OF FAMILIAL ADENOMATOSIS POLYPOSIS

Pilmatrixoma is a benign neoplasm that arises from hair matrix cells and usually occurs as a solitary lesion. Solitary pilomatrixoma frequently harbors activating mutations in the B-catenin gene, leading to inhibition of B-catenin degradation and accumulation of nuclear B-catenin, which activates the WNT pathway and drives tumor formation. Multiple pilomatrixomas are rare, but can be seen in several conditions including familial adenomatous polyposis (FAP). The APC gene product is important in ubiquitin-mediated degradation of B-catenin; therefore some mutations of APC interfere with B-catenin degradation resulting in WNT activation and tumor formation, including formation of pilomatrixoma, colon cancer and other WNT driven tumors. We describe the case of an 11-year-old girl who developed multiple pilomatrixomas on her head, neck and trunk 3 years following the diagnosis and treatment of a WNT+ medulloblastoma. Her family medical history is unknown due to being adopted from the Philippines. Because of the known association of multiple pilomatrixomas and FAP, and the known association of medulloblastoma and FAP, she underwent genetic testing and was found to have a pathogenic germline mutation of the APC gene (c.595dupG (p.Ala199Glyfs*53)) which is consistent with a diagnosis of autosomal dominant familial adenomatous polyposis. The patient will now undergo regular surveillance for FAP related cancers, which may be potentially lifesaving. This is the first reported case of multiple pilomatrixomas in association with medulloblastoma.