Post-transplant malignancy in Thai kidney recipients: a single-center cohort study on incidence, risk factors, and outcomes

Malignancy is a major cause of morbidity and mortality in kidney transplant recipients (KTRs), who carry an elevated risk compared to the general population. This study aimed to investigate the incidence, risk factors, and outcomes associated with the development of de novo malignancy among adult KTRs at a single center. This retrospective cohort study analyzed data from 292 adult patients who underwent their first kidney transplantation at Siriraj Hospital, Mahidol University, between January 2014 and December 2018. Patients with a history of prior organ transplantation or pre-existing malignancy before kidney transplantation were excluded. The cohort comprised 292 KTRs with a median age at transplantation of 44.0 (36.0–52.0) years and a median follow-up of 8.7 (7.5–9.8) years. Overall, 20 recipients (6.8%) developed de novo malignancies, with a median time to diagnosis of 4.0 (2.7–5.9) years. The standardized incidence ratio (SIR) for all malignancies was 3.71 (95% CI: 2.27–5.73). Urothelial cancer was the most common malignancy, observed in 5 cases (25%; SIR 53.11, 95% CI: 17.25–123.95), and was particularly prevalent in female patients. Post-transplant lymphoproliferative disorder (PTLD) was the second most frequent malignancy, diagnosed in 3 cases (15%; SIR 16.60, 95% CI: 3.42–48.51). Renal cell carcinoma, breast cancer, and prostate cancer each accounted for 2 cases (10%), with significantly elevated SIRs for renal cell carcinoma (34.75) and prostate cancer (14.20). The remaining malignancies, each observed in a single case (5%), included lung cancer, cutaneous squamous cell carcinoma, liposarcoma, cholangiocarcinoma, nasopharyngeal cancer, and chronic myeloid leukemia. No clinical factor was significantly associated with post-transplant malignancy on univariate analysis. Following diagnosis, 11 recipients (55.0%) were converted to an mTOR inhibitor-based regimen. Patient survival was significantly worse among recipients who developed malignancy (5-year survival 85.0% vs. 93.0%; Log-rank P = 0.023), whereas death-censored graft survival did not differ between groups ( P = 0.831). Five patients (25.0%) with malignancy died, of whom four died from cancer and one from infection. Kidney transplant recipients carry a significantly elevated risk of de novo malignancies, with urothelial cancer being the most common type observed in this cohort. Malignancy was associated with reduced patient survival but not with graft loss. Our results highlight the critical importance of vigilant cancer screening and continuous monitoring in KTRs to ensure early detection and effective management.