HRH1 and cancer: Activation of HRH1 suppresses the transcription of tumor suppressor genes such as insulin‐like growth factor II receptor (IGF‐IIR) and the anti‐angiogenic matrix protein fibulin‐5 (FBLN5), leading to decreased intracellular protein levels and reduced availability in the plasma membrane and extracellular matrix, respectively.[98] Moreover, clinical evidence indicates that pre‐existing allergic conditions or high histamine levels can dampen immunotherapy responses, conversely, cancer patients who took antihistamines during immunotherapy had significantly improved survival outcomes.