Aggressive Behaviour of Merkel Cell Carcinoma in a Kidney Transplant Patient Receiving Tacrolimus Treatment – Is There an Alternative in Immune Checkpoint Inhibitor Treatment?

Background: Merkel cell carcinoma (MCC) is a rare skin neoplasm first described by Toker in 1972. The tumor usually presents in the sixth to seventh decade of life as a solitary reddish-brown to violaceous subcutaneous nodule on the head, neck, or the extremities. It is seen at an earlier age only in immunocompromised patients like transplant patients in immunosuppressive therapy. Thus, cancer has now become the second cause of death among transplant patients. The tumor growth is rapid in MCC patients, and for metastatic disease, no substantial benefit is obtained by chemotherapy. A new drug has recently become available, an immune checkpoint inhibitor (CPI), avelumab, that is able to delay disease progression significantly. However, there are no current guidelines for the use of immune checkpoint inhibitors in transplant patients. Case Presentation: We describe the case of a 55-year-old kidney transplant patient on immunosuppressive therapy with tacrolimus with an early occurrence of a Merkel cell carcinoma whose aggressive behaviour could not be hampered by Avelumab, due to fear of allograft rejection. Conclusion: CPI therapy is potentially lifesaving in advanced MCC. Further studies are urgently needed to test its benefit in this rapidly expanding field of post-transplant malignancies where there are only a few and less effective therapeutic options.