Loss of GPER Identifies New Targets for Therapy among a Subgroup of ERα-positive Endometrial Cancer Patients with Poor Outcome.

Background: The G protein-coupled oestrogen receptor, GPER, has been suggested as an alternative oestrogen receptor. Our purpose was to investigate the potential of GPER as a prognostic and predictive marker in endometrial carcinoma and to search for new drug candidates to improve treatment of aggressive disease. Materials and method: A total of 767 primary endometrial carcinomas derived from three patient series, including an external dataset, were studied for protein and mRNA expression levels to investigate and validate if GPER loss identifies poor prognosis and new targets for therapy in endometrial carcinoma. Gene expression levels, according to ER α /GPER status, were used to search the connectivity map database for small molecular inhibitors with potential for treatment of metastatic disease for receptor status subgroups. Results: Loss of GPER protein is significantly correlated with low GPER mRNA, high FIGO stage, non-endometrioid histology, high grade, aneuploidy and ER α loss (all P -values ⩽0.05). Loss of GPER among ER α -positive patients identifies a subgroup with poor prognosis that until now has been unrecognised, with reduced 5-year survival from 93% to 76% ( P =0.003). Additional loss of GPER from primary to metastatic lesion counterparts further supports that loss of GPER is associated with disease progression. Conclusion: These results support that GPER status adds clinically relevant information to ER α status in endometrial carcinoma and suggest a potential for new inhibitors in the treatment of metastatic endometrial cancers with ER α expression and GPER loss.