Furthermore, the results of an in vitro experiment11 demonstrated the anti-tumor effects of tramadol, which could be explained by complex mechanisms including suppression of colony formation, cell cycle arrest, induction of apoptosis, regulation of ER and PR expression, and potential antagonist-like actions on 5-hydroxy tryptamine (HT)2B receptor and TRPV1. The gene discussed is ESR1; the disease is neoplasm.