GPRC5A and breast cancer: Initial efforts indicate that at least certain of the GPCRs we have identified are functional in cancer cells [e.g., GPR161 in breast cancer (Feigin et al., 2014) and GPRC5A in pancreatic cancer (Zhou et al., 2016)] and in the microenvironment (e.g., GPR68; Wiley et al., 2018).