HTR3A and cancer: The expression of serotonin receptor HTR3A was found increased by fivefold in lung carcinoma; no direct link has been reported between HTR3A and lung adenocarcinoma, yet; however, nucleotide polymorphisms of this gene have been related to opioid- or nausea/vomiting signaling pathways in cancer patients [63] and to bowel syndrome [64].