Opioids represent a major source of relief from pain. However, opioid abuse may cause immunosuppression and cancer. We have recently reported results on novel non-peptidic delta- and mu-selective opioids that induced immunopotentiation of T cell and macrophage functions in vitro and ex vivo. In the present study, the effects of the delta-opioid receptor agonist and potent analgesic (+)-4-((alpha R)-alpha-((2S, 5R)-4-allyl-2, 5-dimethyl-1-piperazinyl)-3-methoxybenzyl)-N, N-diethyl-benzamide (SNC80) on in vitro and in vivo tumor cell growth were investigated using the L5178Y-R murine model. SNC80 marginally, but significantly (p < 0.05), inhibited (up to 14%) the in vitro growth of L5178Y-R tumor cells. However, in vivo intratumor administration of SNC80 (2 and 4 mg/kg) reduced up to 60% L5178Y-R tumor-bearing Balb/c mice death, and significantly (p < 0.05) reduced tumor weights (up to 73% reduction) in these animals. This study may support the evaluation of SNC80 in preclinical and clinical studies.