HRH1 and cancer: HRH1 knockout or antihistamine treatment reversed macrophage‐mediated immunosuppression, restored T cell cytotoxic activity, and enhanced immunotherapy efficacy.[99] In addition, recent studies have highlighted a novel role of histamine receptor H4 (HRH4) in cancer progression, identifying it as a promising molecular target for anticancer drug development,[100] including in melanoma.[101] Preclinical data further provided evidence that HRH4 agonists generate significant in vivo antitumor effects,[102] although further studies are needed to elucidate their therapeutic potential.