Risk of Malignancy with Immunosuppressive Drugs Used in Organ Transplants Compared to Those Used for Non-Transplant Indications

Background: Immunosuppressive drugs (ISDs) are essential for preventing organ rejection but have been reported to increase cancer risk with prolonged use. This study compares cancer risk between ISDs used for long-term maintenance after transplantation (T-ISDs) and those prescribed for non-transplant chronic conditions including cell-mediated (C-ISDs) and receptor-mediated (R-ISDs) ISDs. We hypothesized that cancer risk would differ between T-ISDs and both C-ISD and R-ISD groups. Methods: Using the TriNetX database, solid organ transplant recipients treated with tacrolimus (TAC), cyclosporine (CY), rapamycin (RAPA), or mycophenolate (MMF) were compared to propensity-matched R-ISDs (adalimumab, infliximab, etc.) or C-ISDs (methotrexate, azathioprine, etc.) for at least 24 encounters to determine risk of malignancy. Hazard ratios (HRs) with 95% confidence intervals (CIs) were calculated to assess the three-year cancer risk. Results: After matching, T-ISDs were associated with higher malignancy risk compared to both R-ISDs (n = 29,748; HR 2.616, 95% CI 2.427–2.820) and C-ISDs (n = 31,704; HR 1.271, 95% CI 1.195–1.351). Each individual immunosuppressant in the T-ISD cohort was associated with increased cancer risk compared to R-ISDs, while only TAC and CY showed higher risk than C-ISDs (TAC: n = 9846, HR 1.354, 95% CI 1.228–1.492; CY: n = 1801, HR 1.234, 95% CI 1.007–1.512). Organ-specific analyses showed consistent patterns across systems. Conclusions: Overall, T-ISDs are associated with increased malignancy risk compared to R-ISDs and modestly compared to C-ISDs. TAC and CY confer the greatest risk, while MMF demonstrates relatively lower relative risk. These findings underscore the need to individualize ISD regimens to minimize long-term cancer risk.