Abstract
Merkel cell carcinoma (MCC) is a rare but aggressive skin cancer with frequent metastasis and death. MCC has a mortality rate of 30%, making it more lethal than malignant melanoma, and incidence of MCC has increased almost fourfold over the past 20 years in the USA. MCC has long been considered to be an immunogenic cancer because it occurs more frequently in immunosuppressed patients from organ transplant and HIV infection than in those with immunocompetent. Chronic UV light exposure and clonal integration of Merkel cell polyomavirus (MCPyV) are two major causative factors of MCC. Approximately 80% of MCC are associated with MCPyV, and T cells specific for MCPyV oncoproteins are present in the blood and tumors of patients. Several studies have shown that a subset of MCCs express PD-1 on tumor-infiltrating lymphocytes and express PD-L1 on tumor cells, which suggests an endogenous tumor-reactive immune response that might be unleashed by anti-PD-1 or anti-PD-L1 drugs.
Highlights
Merkel cell carcinoma (MCC) is a rare but highly aggressive neuroendocrine skin cancer, which was described for the first time in 1972 as trabecular carcinoma of the skin [1]
Merkel cell polyomavirus (MCPyV) isolated from MCCs, in contrast with MCPyV from non-tumor sources, present mutations that are responsible for the premature truncation of the MCV large T (LT) helicase [43, 44]
Advanced MCC is generally considered to be sensitive to chemotherapy, but responses are transient, offering a median progression free survival (PFS) of only 3 months [55]
Summary
Merkel cell carcinoma (MCC) is a rare but highly aggressive neuroendocrine skin cancer, which was described for the first time in 1972 as trabecular carcinoma of the skin [1]. MCPyV isolated from MCCs, in contrast with MCPyV from non-tumor sources, present mutations that are responsible for the premature truncation of the MCV LT helicase [43, 44] These mutations do not affect the Rb binding domain, but eliminate the capacity of the viral DNA to replicate. MCPyV-negative MCC is among the most mutated of all solid tumors, including melanoma [18, 48,49,50] These mutations are mostly UV-signature mutations, such as p53 and Rb, commonly resulting in loss of functional protein expression [18, 49]. Adjuvant Therapy of Completely Resected Merkel Cell Carcinoma with Immune Checkpoint Blocking Antibodies Versus Observation (ADMEC-O)
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