Germline EGFR mutation and cancer predisposition in adolescent and young adult (AYA) females with adrenocortical carcinoma.

e13014 Background: Adrenocortical Carcinoma (ACC) is a rare endocrine tumor with poor overall prognosis and slight overrepresentation in females. In children, ACC is associated with inherited cancers, predominantly Li-Fraumeni syndrome, with 50-80% of childhood ACC harboring TP53 germline mutations. ACC in AYA are rarely due to germline TP53 mutations; IGF2, PRKAR1A and MEN1 are other less common germline mutated genes in this age group. Methods: We analyzed exome sequencing data from 21 children (C, < 15y), 32 AYA (15-39y), and 60 adult patients ( > 39y) with ACC, originating from the Cleveland Clinic, and TCGA and St. Jude’s datasets. We utilized the Integrative Variant Analysis platform to classify variants based on the American College of Medical Genetics guidelines. We retained all pathogenic, likely pathogenic, and highly-prioritized Variants of Uncertain Significance. Results: Pathway analysis on prioritized variants showed EGFR and p53 pathways as the two top pathways among our C-AYA patients. We found that 4.8% of children and 6.2% of AYA, all female patients, harbored a non-kinase-domain germline EGFR mutation, compared to only 1.7% of adult patients with ACC. As proof-of-principle functional validation, we engineered a lentiviral-mutant stable ACC-cell line, harboring an EGFR variant from a 21 y/o female with aggressive bilateral ACC (p.Asp1080Asn), without germline TP53 mutation. We showed that mutant cells grow slower, yet migrate faster and are characterized by a stem-like phenotype compared to wildtype cells. Osimertinib, among all tested EGFR inhibitors, resulted in the highest growth inhibition of mutant cells. While EGFR inhibitors had no effect on the stemness of mutant cells, Sunitinib, a multi-receptor tyrosine kinase inhibitor, significantly reduced the stem-like behavior. Conclusions: Our data suggest that EGFR is a novel underlying germline predisposition factor for ACC, especially in the female C-AYA population. Although our pre-clinical observations need to be further validated, identifying a targetable gene for ACC has the potential to improve precision oncology management of this disease, which is known to have limited therapeutic options.