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Medulloblastomas associated with APC germline pathogenic variant share the good prognosis of CTNNB1 mutated medulloblastomas.

BACKGROUND
Medulloblastomas may occur in a predisposition context, including familial adenomatosis polyposis. Medulloblastomas related to APC germline pathogenic variant remain rare and poorly described. Their similarities with sporadic WNT medulloblastomas still require to be described.


METHODS
We performed a multicentric retrospective review of 12 patients treated between 1988 and 2018 for medulloblastoma with identified or highly suspected (personal of familial history) APC germline pathogenic variant. We report personal and familial history, APC gene pathogenic variant whenever available, clinical and histological characteristics of the medulloblastoma, treatments, and long-term outcome including second tumor and late sequelae.


RESULTS
Medulloblastomas associated with APC pathogenic variant are mainly classic (11/11 patients, 1 NA), non-metastatic (10/12 patients) medulloblastomas, with nuclear immunoreactivity for ß-catenin (9/9 tested cases). 10/11 assessable patients are disease-free with a median follow-up of 10.7 years [1-28]. Secondary tumors included desmoid tumors in 7 patients (9 tumors), 1 thyroid carcinoma, 2 pilomatricomas, 1 osteoma, 1 vertebral hemangioma, and 1 malignant Triton in the radiation field which caused the only cancer-related death in our series.


CONCLUSIONS
Medulloblastomas associated with APC pathogenic variant have an overall favorable outcome, even for metastatic tumors. Yet, long-term survival is clouded by second tumor occurrence; treatment may play some role in some of these second malignancies. Our findings raise the question of applying de-escalation therapeutic protocol to treat patients with APC germline pathogenic variant given the excellent outcome, and reduced intensity of craniospinal irradiation may be further evaluated.