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After decades of successful organ transplantation clinicians continue to be troubled by the increasing incidence of cancers under maintenance immunosuppression. In this study, we examined rates of malignancies in 2419 renal transplant recipients transplanted in our institution between 1978 and 2005. In renal transplant recipients the cumulative incidence of cancer after 25 years was 49.3% for all tumors and 39.7% excluding non-melanoma skin cancers, compared with 21% for a normal sex- and age-matched population. The most frequent tumors observed were non-melanoma skin cancers (20.5%), kidney cancers (12.0%), and cancers of the pharynx, larynx, or oral cavity (8.2%). The general increase of cancer risk was 4.3-fold. Independent risk factors for the development of a tumor were male gender, older recipient age, the presence of preformed antibodies before transplantation, and the time on immunosuppression. Interestingly, the use of IL-2-receptor antagonists significantly reduced the tumor risk of transplant recipients. The tumor risk between immunosuppressive drugs typically used for maintenance immunosuppression was not significantly different. However, mammalian target of rapamycin (mTOR) inhibitor-based immunosuppressive protocols showed a clear tendency for lower malignancy rates. De novo malignancies following renal transplantation represent a serious problem endangering the prognosis of otherwise successfully transplanted patients. Future studies will have to address whether optimized immunosuppressive regimens including mTOR-inhibitors are capable of reducing the incidence or preventing the development of posttransplant malignancies.

In recent years, clusters of Pneumocystis jirovecii (formerly Pneumocystis carinii) pneumonia (PCP) among immunocompromised individuals have been reported. Mostly, the source of infections was suspected to be within the clinical settings when transplant recipients and PCP patients shared hospital facilities. We report on a cluster of 16 renal transplant recipients positive for P. jirovecii. None of them received anti-Pneumocystis prophylaxis prior to P. jirovecii detection. Epidemiological studies revealed that 15 of them had received kidney transplants at a German university hospital and attended the same inpatient and outpatient clinic from January through September 2006. Multilocus sequence typing (MLST) was performed on the following genes: ITS1, ␤-tub, 26S, and mt26S. P. jirovecii DNA was available from 14 patients and showed identical MLST types among these renal transplant recipients. Surprisingly, one patient who was treated at a different nephrological center and reported no personal contact with patients from the renal transplantation cluster harbored an identical P. jirovecii MLST type. Three HIV-positive patients and one bone-marrow-transplanted hematologic malignancy patient-treated at different medical centers-were used as controls, and different MLST types were revealed. Interestingly, in three of the four previously described regions, new alleles were detected, and one new polymorphism was observed in the mt26S region. The epidemiological data and the genotyping results strongly suggest a nosocomial patient-to-patient transmission of P. jirovecii as the predominant transmission route. Therefore, strict segregation and isolation of P. jirovecii-positive/ suspected patients in clinical settings seems warranted.

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