A. Immune checkpoint molecules exist on the surface of T lymphocytes and are only expressed in pathologic conditions such as cancer B. The site of action of monoclonal antibodies blocking CTLA-4 expression is in lymphoid tissue, whereas monoclonal antibodies that block PD-1 or its ligands, are in the tumor C. Programmed death ligand-1 expression is exclusively induced by oncogenic mutations such as PI3K, and expression of PD-L1 in the tumor microenvironment has a strong linear correlation with response to immune checkpoint blockade D. Treatment with immune checkpoint blockade is approved only for the treatment of patients with stage IV (metastatic) cancer E. Unsure

A. A high density of CD8+ T cells at the invasive margin of a tumor (in a pre-treatment tumor biopsy) is associated with a higher likelihood of response to immune checkpoint blockade B. High expression of PD-L1 in the tumor microenvironment is associated with a higher likelihood of response to checkpoint blockade, whereas response rates are essentially zero with negative PD-L1 expression C. Microsatellite instability status was one of the first FDA-approved biomarkers to help guide treatment with immune checkpoint blockade, and total mutational burden is an approved biomarker for patients with melanoma going onto immune checkpoint blockade D. Turnaround time for biomarker assessment via immunohistochemistry is 1-2 days, which is similar for next generation sequencing approaches (also 1-2 days) however there is a significant cost differential between the 2 approaches E. Unsure