Viral- and nonviral-mediated delivery of genes for the μ-opioid receptor and the endothelin B receptor (OPRM1 and EDNRB, respectively) produce endogenous analgesia through the secretion of opioids by the carcinoma in preclinical oral cancer pain models (Viet et al., 2011; Yamano et al., 2017). Here, OPRM1 is linked to carcinoma.