In a retrospective study we analyzed the incidence and characteristics of de novo tumors developing in renal transplant recipients treated in our center. The 5% incidence de novo tumors developing among patients treated with azathioprine and prednisolone (n = 241) was similar to the 5.4% incidence of de novo tumors developing among patients treated with calcineurin-based immunosuppression (n = 1918). The most common malignancies among our patients were basal cell (21.7%) and squamous cell (13.9%) carcinomas of the skin, followed by urogenital (10.4%) and lung malformations (9.6%). A high incidence of Kaposi's sarcoma (9.6%; half cutaneous and half visceral) and a lower than expected incidence of posttransplant lymphoproliferative disorder (PTLD; 3.5%) was found. Among patients developing de novo tumors, the incidence of death with a functioning graft was higher than among recipients without tumors. Moreover, the incidence of tumor-related death was high among the de novo tumor recipients. Among our recipients, the most aggressive tumors were Kaposi's sarcoma, lung tumors, lymphomas, and gastrointestinal tumors, which occurred relatively early after transplantation and were the cause of death in most cases. Compared to tumor registry data, we found an inverse basal-to-squamous cell carcinoma ratio, a lower incidence of PTLD, and a higher incidence of Kaposi's sarcoma.
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