To analyze the incidence and clinical characteristics of de novo malignancies in kidney transplant recipients.

We retrospectively reviewed the clinical data of 9, 000 recipients who underwent kidney transplantation at the Kidney Disease Center, the First Affiliated Hospital, Zhejiang University School of Medicine, between May 1988 and January 2025. Recipients were categorized into a malignancy group (n=485) and a non-malignancy group (n= 8 515) according to whether de novo malignancy occurred after transplantation. We assessed the incidence, tumor types, and time to onset of de novo malignancies, as well as the number and proportional distribution of malignancy events diagnosed during 1988-2000, 2001-2015, and 2016-2025. Between-group comparisons were performed using independent-samples t tests for normally distributed continuous variables, Mann-Whitney U tests for non-normally distributed continuous variables, and χ² tests or Fisher's exact test for categorical variables. P<0.05 was considered statistically significant.

Compared with the non-malignancy group, recipients in the malignancy group were older at transplantation [(43.6±10.9) vs. (38.1±11.3) years], more likely to be female (42.1% vs. 34.2%), and more likely to have received a kidney from a deceased donor (87.2% vs. 68.5%), all differences were statistically significant (t/χ²=10.426, 12.378, and 75.746, all P<0.05). During follow-up, the overall incidence of de novo malignancy after kidney transplantation was 5.39% (485/9 000); the incidence was 4.78% (281/5 880) in men, 6.54% (204/3 120) in women, and 1.21% (3/247) in children. Among the 485 recipients with de novo malignancies, 505 malignancy events were diagnosed. Digestive system tumors were the most common (121 events, 24.0%), followed by urinary system tumors (87 events, 17.2%), thyroid cancer (70 events, 13.9%), lung cancer (61 events, 12.1%), and post-transplant lymphoproliferative disorder (PTLD) (49 events, 9.7%). The mean age at diagnosis was (52.7±12.0) years, and the median time from transplantation to diagnosis was 91 (2-416) months. Kaposi sarcoma occurred earliest, with a median onset of 38 (12-205) months after transplantation. PTLD showed a bimodal distribution, with a median onset of 105 (2-301) months; early-onset cases (within 1 year after transplantation) accounted for 18.4%. All 3 malignancies in pediatric recipients were PTLD, all occurring within 1 year after transplantation (4-11 months). Solid organ tumors (lung cancer, digestive system tumors, and urinary system tumors) occurred later, with median onset times all >80 months. The numbers of de novo malignancy events diagnosed after kidney transplantation during 1988-2000, 2001-2015, and 2016-2025 were 96, 278, and 131 events, respectively.

The incidence of de novo malignancies after kidney transplantation is significantly higher than that in the general population, with digestive system tumors being the most common. Given the distinct temporal patterns in the onset of different tumor types, phased follow-up and screening strategies based on risk windows should be implemented for high-risk populations.