GPR68 and breast cancer: Assessment of these two acid sensors across the four major breast cancer subtypes (PAM50 classifications) revealed that both OGR1 and TDAG8 were significantly higher in cancers compared with normal breast tissue (Figures 3A and 3B), wherein OGR1 appeared to be more strongly associated with breast cancer disease progression compared with TDAG8 (Figures S4B and S4C).