Abstract
Recent findings: Merkel cell carcinoma (MCC) is a rare, highly aggressive, neuroendocrine cancer of the skin, associated with immunosuppression, Merkel cell polyoma virus (MCPyV) infection and UV-carcinogenesis. Whilst impressive and durable responses to immune checkpoint inhibitors have revolutionised the treatment of advanced MCC, approximately 50-70% of patients have either primary or acquired resistance to immune checkpoint blockade and robust predictive biomarkers of response are yet to be identified. Exploratory subgroup and biomarker analyses from clinical trials and retrospective studies have evaluated multiple clinical characteristics including age, performance status, immunosuppression, prior therapy, baseline and response imaging assessments, and molecular features including MCPyV status, programmed death ligand-1 (PD-L1) expression, tumour mutational burden (TMB) and tumour infiltrating lymphocytes as potential markers of response.
Summary: Better performance status, earlier line of therapy and early 18FDG-PET response have been consistently associated with favourable response to immune checkpoint inhibitors in MCC. High response rates are seen regardless of viral status, TMB and PD-L1 status.
Purpose of the review: We provide a review of clinical, imaging and molecular markers of response to immune checkpoint inhibitor therapy in MCC to aid patient selection and personalization of therapy.
Keywords
Merkel cell cancer, Immunotherapy, Immune checkpoint inhibitors, Biomarkers, FDG-PET, Merkel Cell Polyoma Virus, Tumour mutational burden, Programmed death ligand-1