The Comparative Effect of Morphine on Proliferation of Cancer Cell Lines Originating from Different Organs: An In Vitro Study.

Background/Objectives: Opium consumption was recently classified by the International Agency for Research on Cancer (IARC) monograph as carcinogenic to humans based on strong evidence for cancers of the larynx, lung, and urinary bladder, and limited evidence for cancers of the oesophagus, stomach, pancreas, and pharynx. This poses the question of a potential pro-cancer effect of pharmaceutical opioid analgesics. In vitro studies employing a variety of experimental conditions suggest that opioid alkaloids have proliferative or antiproliferative effects. We set out to reconcile this discrepancy and explore the hypothesis that opioids promote cancer cell proliferation in an organ-dependent fashion. Methods: Using strictly controlled conditions, we tested the effect of morphine on the proliferation of a series of human cancer cell lines isolated from organs where cancer risk was linked causally to opium consumption in human studies (i.e., lung, bladder, and larynx), or control organs where no link between cancer risk and opium consumption has been reported in human studies (i.e., breast, colon, prostate). Results: Our results showed a minimal effect on proliferation on any cell line and no trend supporting an organ-specific effect of morphine. Conclusions: This argues against a direct effect of opioids on tumour cell proliferation to support their organ-specific effect.