Incidence of Merkel cell carcinoma in renal transplant recipients

Background. The risk factors for Merkel cell carcinoma (MCC), a rare type of skin cancer, are poorly understood. Some evidence suggests that MCC is more common in individuals with abnormal immune function resulting from viral infection, autoimmune disease or organ transplantation. Methods. The national Renal Transplant Registry and the Finnish Cancer Registry data were searched for recipients of a renal transplant who were diagnosed with MCC. The MCC diagnoses were confirmed using immunohistochemistry. Results. Three cases of MCC were detected among 4200 individuals who underwent renal transplantation from 1967 to 2005 [expected number 0.05, standardized incidence ratio (SIR) 66, 95% CI 14-194, P < 0.001]. The latency period between the transplant and detection of MCC ranged from 6 to 19 years. In all three cases, the cause of transplantation was an autoimmune disease. All three died from aggressive MCC with a survival time ranging from 0.5 to 2.1 years. Conclusions. The results indicate that the risk of MCC is greatly increased among subjects who have undergone renal transplantation. The course of the disease appears aggressive in this patient population. The physicians who treat recipients of a kidney transplant should be aware of the substantially increased risk of MCC.