HRH4 and breast cancer: In this regard, numerous studies of the H4R protein expression and its localization have already been performed in different types of cancers including ESCC, GC, CRC, CHOL, breast cancer and melanoma (Medina et al., 2008; Fang et al., 2011; Meng et al., 2011; Zhang et al., 2012; Wang et al., 2014; Massari et al., 2017; He et al., 2018).