We will map and evaluate published evidence regarding (1) opioid concentration data from human subjects with cancer, yielding a “physiologic range” to better interpret available preclinical data, (2) patterns of opioid exposure and disease and treatment-related patient outcomes, and (3) the influence of opioids and μOR activity on cancer cell survival and growth, as well as changes in susceptibility to clinically used chemotherapeutics. This evidence concerns the gene OPRM1 and cancer.