Merkel cell carcinoma (MCC) is a rare skin cancer with a high propensity for recurrence. Persons with chronic immunosuppression have a higher risk of developing MCC and a more aggressive disease course. Immunotherapy treatment enhances the immune system’s ability to fight MCC and is associated with improved disease-specific survival. However, the immunotherapy efficacy in immunosuppressed MCC patients is not well categorized. This study explores and aims to compare differences in immunotherapy efficacy between different forms of immunosuppression, and between immunocompetent versus immunosuppressed MCC patients. In this project, I determined the patient cohort from a Seattle-based prospective registry of 1,529 MCC patients and identified 36 patients treated with immunotherapy and who had chronic immunosuppression. I collected treatment response data from medical records, and analyzed the results. Of the 36 patients, 13 patients (36%) had a complete response (CR), 3 patients (8%) had a partial response (PR), and 20 patients (56%) had progressive disease (PD). Disease progression and survival status varied greatly among different types of immunosuppression. Five types of chronic immunosuppression were represented in these 36 patients and were evaluated for an objective response (CR or PR): chronic lymphocytic leukemia (CLL, 3/13, 23%), autoimmune disorders (AD, 3/9, 33%), solid organ transplant (SOT, 2/4, 50%), HIV/AIDs (2/3, 67%), and other hematologic malignancies (OHM, 6/7, 86%). In comparison, in a study of immunocompetent patients, 28 of 50 (56%) had objective responses to immunotherapy. Toxicities were also high in immunosuppressed patients, as 9/36 (25%) patients stopped treatment due to toxicities. Immunotherapy efficacy in patients with chronic immunosuppression appears to be dependent on the type of immunosuppression. While there is reason for optimism for patients with certain types of immunosuppression, MCC treatment for patients with CLL remains a major concern.