The in vivo administration of histamine or H4R agonists diminished the tumour growth of human TNBC developed in immune-deficient nude mice with MDA-MB-231 cells.21,22 Importantly, we have recently demonstrated a novel role of H4R in the antitumour immunity of breast cancer,23 which could affect the clinical therapeutic outcomes of histamine-related pharmacological compounds. This evidence concerns the gene HRH4 and breast cancer.