Merkel Cell Carcinoma in Kidney Transplant Recipients

Merkel cell carcinoma (MCC) is an uncommon form of skin neoplasm with poor histological differentiation and an aggressive disease process, leading to high recurrence and mortality. There are multiple risk factors in which being in an immunocompromised state is a significant factor, and the discovery of Merkel cell polyomavirus (MCPyV) since 2008 has strengthened causal associations between MCC and immunosuppression. Individuals who have undergone kidney transplantation are therefore more susceptible to having MCC, secondary to post-transplant immunosuppression which plays a vital role in reducing the risk of transplant kidney rejection. Over recent years a rise in the incidence of MCC following kidney transplantation is noted, with increased reporting of such cases. Whilst localized MCC is observed, MCC metastasis to the lymphatic system, brain, bone, liver, lung, and heart has been previously observed in patients with transplanted kidneys. Kidney metastasis is less common and has been only reported in recent years with greater frequency. The management of aggressive, metastatic MCC has historically been palliative, and prognosis is poor. Recently, the use of immune checkpoint inhibitors for metastatic MCC in multi-center phase II clinical trials have shown promising survival outcomes and have been approved for use in countries such as the United States as a first-line treatment. In this review we will explore the potential pathophysiological processes of MCC manifesting post-kidney transplantation. We will then evaluate the epidemiology of MCC within the context of kidney transplantation, before discussing the various clinical presentations, diagnostic measures, surveillance strategies, and current treatment options as well as future directions to best manage MCC in kidney transplant recipients.