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Rare variants in MAGEC3, members of the melanoma antigen gene family, are associated with BRCA-independent early onset ovarian cancers, while somatic mutations of this gene have been associated with kidney cancers. In this report, we quantified normal and tumor protein expression of MAGEC3 via immunohistochemistry in N=394 ovarian cancers and N=220 renal cell carcinomas. MAGEC3 protein levels fell into two categories – normal MAGEC3 and MAGEC3 loss – characterized by expression equivalent to normal tissue or significantly lower than normal tissue, respectively. Interestingly, cases with MAGEC3 loss demonstrated better overall survival in both ovarian cancers and renal cell carcinomas, which resembles patient outcomes with BRCA2 loss. MAGEC3 protein expression was associated with upregulation of pathways regulating G2/M checkpoint (NES: 4.13, FDRSTATEMENT OF TRANSLATIONAL RELEVANCEMAGEC3 protein is expressed in multiple tissues and is dysregulated in cancer. In this work, we show that ovarian and kidney cancer patients with loss of MAGEC3 protein have favorable prognosis, indicating that MAGEC3 protein level may be used as a prognostic biomarker. Integrative genomic analysis of patients spanning more than nine cancer types showed an association between MAGEC3 protein and genes affecting stress response, including those involved in cell cycle and DNA damage repair. Additionally, it is correlated with tumor mutational burden in patients with mutated oncogenes. These associations suggest that MAGEC3 protein levels may be used to identify patients with deficient DNA damage repair mechanisms that can be targeted by PARP inhibitors. To operationalize this idea, we use machine learning to predict MAGEC3 protein levels from RNA sequencing data which can facilitate the identification of patients for treatment stratification according to their MAGEC3 status. |
