An Unusual Aggressive Skin Cancer in a Kidney Transplant Recipient

Introduction: Merkel cell carcinoma (MCC), a rare and aggressive neuroendocrine skin cancer, has a poor prognosis in immunocompromised patients. In advanced stages, radiotherapy, chemotherapy, and immunotherapy have been used with variable success. Immunotherapy is relatively contraindicated in transplant recipients due to the risk of allograft rejection and loss. We report a complex case of aggressive metastatic MCC in a kidney transplant recipient (KTR). Case Description: A 66-year-old female with ESKD due to hypertension receiving a kidney transplant 4 years prior was diagnosed with stage IIIB MCC of the left wrist (Figure 1A). Her disease progressed rapidly despite undergoing radical local resection and axillary dissection. Within a month post excision, she had developed numerous new MCC lesions on her left arm and axilla which were deemed unresectable and had a suboptimal response to radiotherapy. After deliberation, immunotherapy with pembrolizumab was initiated, but stopped after 4 cycles (of 35 planned) due to extensive disease progression (Figure 1B) and patient progressed to hospice care. Throughout her pembrolizumab course, she remained on prednisone, low dose tacrolimus, and mycophenolate. She had no episodes of rejection and maintained good allograft function. Discussion: Indications for checkpoint inhibitors in the treatment of malignancies are growing. Pembrolizumab, a PD-1 ligand blocker, enables lymphocytes to target and destroy cancer cells. KTRs are often excluded from checkpoint inhibitor trials due to the risk of allograft loss (40-70% incidence). Despite this risk, KTRs can benefit from immunotherapy to treat aggressive malignancies such as MCC. In our patient, we elected to continue immunosuppression along with pembrolizumab to balance the risk of rejection and anti-cancer effect. Although immunosuppression protected the graft, it may have compromised immune-mediated tumor regression. Our case supports the literature that pembrolizumab can be utilized in certain settings in KTRs without graft loss and highlights the need for additional research for the optimal management of aggressive cancers in KTRs.