De novo cancer in patients on dialysis and after renal transplantation: north-western Italy, 1997-2012.

Background: Kidney transplant recipients (KTR) are known to have a higher risk of cancer than the general population, especially of malignancies related to oncogenic viral infections. This study assessed the incidence of de novo malignancies (DNMs) in patients receiving kidney transplantation and in dialysis patients (DP) on the waiting list for transplantation at the same centre. The aim was to quantify the contribution of post-transplant immunosuppression to the underlying risk of developing a DNM in dialysis patients on the waiting list for kidney transplant.

Methods: Cancer incidence rates were computed using the Kaplan-Meier product-limit method. The number of DNMs observed in both groups was compared to the expected incidence in the general Italian population through calculation of the standardized incidence ratios (SIR) and their 95% confidence intervals (CI). To identify risk factors, incidence rate ratios (IRR) and 95% CIs were computed using Poisson regression analysis. The comparison of incidence rates between the two cohorts was also performed using age standardized incidence rates (ASR) and their ratio (age standardized rate ratio, ASRR).

Results: In 4858 person-years (PYs) of observation, 75 out of 735 KTR were diagnosed with DNM: 57 solid neoplasms, 13 post-transplant lymphoproliferative disorders (PTLD), and 12 Kaposi sarcomas (KS). The overall incidence was 17.5 cases/10 PYs, resulting in a 2.1-fold increased risk. Twenty-four out of 912 DP, over a follow-up of 2400 PYs, were diagnosed with a solid neoplasm, but none had PTLD or KS. The use of induction therapy after transplant was associated with a significant increased risk of KS (IRR: 3.52; 95% CI 1.04-11.98, p < 0.05). ASRR for all cancers and for solid cancers only was 1.84- and 1.19-fold higher in KTR, respectively, than in the general population. The overall incidence in DP was 10.0 cases/10 PYs, with a 1.6 significantly increased cancer risk compared to the general population.

Conclusion: Our study confirms the increased risk of cancer after transplantation and during dialysis, but showed that virus-related cancers only occur after post-transplant immunosuppression.