Researchers found that in advanced epidermal growth factor receptor (EGFR)-mutant non-small cell lung cancer (NSCLC), the efficacy of PD-1 blockade therapy is low. They looked into whether PD-1 blockade therapy outcomes were linked to patient characteristics, PD-L1 expression, and the presence or absence of immune cells (ICs) in the tumor microenvironment (TME). From January 2016 to March 2018, they looked back at the cases of patients with advanced EGFR-mutant NSCLC who were given PD-1 blockade (nivolumab or pembrolizumab). The tumor proportion score (TPS) for PD-L1 expression and the TME’s composition (CD8, PD-1, CD204, tumoral, and stromal ICs) were analyzed. The TME could be studied in depth in 39 of the 57 EGFR-mutant NSCLC patients who were treated with PD-1 blockade. PD-1 blockade had an ORR of 12.3% in terms of total responses. Median tumoral CD8+ICs: 299/mm2 vs. 115/mm2, P<.01) was the only factor significantly associated with the response. About 5 of the 6 patients (83.3%) who had high PD-L1 expression (TPS:≥50%) and high tumoral CD8+ICs (≥205/mm2) responded to treatment, and they had a significantly longer progression-free survival (PFS) (9.4 months vs. 1.8 months, P<.01). In contrast, there was no response in any of the 7 patients who had high PD-L1 expression and low tumoral CD+ICs (205/mm2). The response and prolonged PFS of PD-1 blockade therapy in EGFR-mutant patients may be predicted by the presence of high levels of PD-L1 expression and high levels of CD8+ ICs in the tumor.