Testosterone therapy and cancer risks among men in the SEER-Medicare linked database

We examined associations between two forms of testosterone therapy (TT) and risks of seven cancers among men. SEER-Medicare combines cancer registry data from the Surveillance, Epidemiology, and End Results programme with Medicare claims. Our population-based case-control study included incident cancer cases diagnosed between 1992-2015: prostate (n = 130,713), lung (n = 105,466), colorectal (n = 56,433), bladder (n = 38,873), non-Hodgkin lymphoma (n = 17,854), melanoma (n = 14,241), and oesophageal (n = 9116). We selected 100,000 controls from a 5% random sample of Medicare beneficiaries and used logistic regression to estimate odds ratios (OR) and 95% confidence intervals (CI). TT was associated with lower risk of distant-stage prostate cancer (injection/implantation OR = 0.72, 95% CI: 0.60-0.86; topical OR = 0.50, 95% CI: 0.24-1.03). We also observed inverse associations for distant-stage colorectal cancer (injection/implantation OR = 0.75, 95% CI: 0.62-0.90; topical OR = 0.11, 95% CI: 0.05-0.24). Risks of distant-stage colorectal and prostate cancers decreased with time after initiating TT by injection/implantation. By contrast, TT was positively associated with distant-stage melanoma (injection/implantation OR = 1.70, 95% CI: 1.37-2.11). TT was not associated with bladder cancer, oesophageal cancer, lung cancer or non-Hodgkin lymphoma. TT was inversely associated with distant-stage prostate and colorectal cancers but was positively associated with distant-stage melanoma. These observations may suggest an aetiologic role for TT or the presence of residual confounding.