HRH4 and breast cancer: Regardless of breast cancer subtype, overexpression of the following mRNAs was observed: HRH1, HRH2, HRH4, HNMT, EDN1, EDNRA, HTR6, GABRB1, ADCYAP1, ADA, and SLC23A2. In turn, the expression profiles of mRNA, GNRH2, and PER2 were reduced in the tumor tissues compared to the controls.