When we examined anti-PD-1 responders and non-responders in metastatic melanoma, we found that responders had a significantly higher correlation between CD3E and PDCD1 than did non-responders, which supports the hypothesis that correlation in expression with CD3E in the tumor microenvironment can be a useful criterion for identifying new therapeutic targets with potential for therapeutic response. The gene discussed is PDCD1; the disease is neoplasm.