PDCD1 and non-small cell lung carcinoma: Given the preclinical and clinical evidence of differences in the tumor immune microenvironment and clinical activity with lead-in and intermittent doses of MEKi with PD-1 blockade in solid tumors, this study was initiated to determine safety, tolerability, and preliminary efficacy of intermittent MEKi with trametinib in combination with pembrolizumab, comparing lead-in trametinib versus lead-in pembrolizumab in NSCLC with an emphasis on KRAS mutant lung cancer.