Some limitations have to be nevertheless acknowledged: (1) The retrospective design; (2) the low rate of events which limits the statistical power of any association; (3) the restricted analysis to stage II or III, non-advanced cancer; (4) the lack of evaluation the OPRM1 gene variant polymorphism and (5) only perioperative opioid use was recorded; (6) no software for IHC evaluation. This evidence concerns the gene OPRM1 and cancer.