GPRC5A and breast cancer: In another study, a mutant allele of GPRC5A was found to affect breast cancer risk (14), as lower levels of GPRC5A had adverse effect on the expression and function of BRCA1. Alterations in gene expression and promoter methylation of GPCRs in tumors have also been reported (10), and these changes appear to promote cancer proliferation, immune evasion, invasion of surrounding tissues, and increased resistance to hostile environments, such as hypoxia (15).