Clinical Impact of Immunotherapy in Merkel Cell Carcinoma patients: A Systematic Review and Meta-Analysis

Background: Immunotherapy is emerging as an alternative for Merkel cell carcinoma (MCC), but its long-term effects on response, survival, and safety are not well established. High-quality evidence is needed to estimate its efficacy and its association with patients and tumor´s characteristics.
Objective: To summarize immunotherapy’s efficacy and safety in MCC patients.
Methods: A systematic review was performed for studies published in MEDLINE, Web of Science, Scopus, and EMBASE. Two reviewers reviewed the literature and data extraction in duplicate. We estimated the proportions for objective responses, progression free survival, overall survival, and treatment-related adverse events (TRAE). Associations between objective response rate (ORR) and immunobiological markers were analyzed.
Results: Six clinical trials of 201 patients treated with immunotherapy were included. The ORR was 51% (95%CI, 0.40-0.62; I2=37.1%) and grade ≥ 3 TRAE was observed in 18% (95%CI, 0.11-0.29; I2=49.5%) of patients. We observed no significant difference between response and immunobiological characteristics.
Conclusions: A significantly reduced tumor diameter with durable response rates and a safe profile are obtained with immunotherapy. Its association with immunobiological markers suggests that it may act on multiple pathways that achieve similar response rates on either tumor subtypes.