Proline, glutamate, and leucine-rich protein 1 (PELP1) are involved in several cancers, but little is known about PELP1 in lung cancer. In this study, PELP1 expression was evaluated in 305 lung cancer (NSCLC) specimens to explore the role of PELP1 in lung cancer. After silencing PELP1, the proliferation, migration, invasion of tumor cells, PELP1 in relation to cell cycle and signaling pathways were evaluated, and whole-genome exons were analyzed. PELP1 is overexpressed in lung cancer, PELP1 expression correlated with squamous carcinoma, smoking, and wild-type EGFR status (all Ps<0.001) but associated with lung cancer-specific survival (P > 0.05). Silencing significantly inhibited lung cancer cell proliferation, migration, and invasion (P < 0.05) and promoted high sensitivity of lung cancer cells to tyrosine kinase inhibitor (TKI) gefitinib. PELP1-silenced cells showed downregulated phosphorylated MAPK, cyclinD1, CDK2, and upregulated RB (P < 0.05) but no change in AKT. In PELP1-silenced lung cancer cells, 140 genes were upregulated, and 143 genes were downregulated. Furthermore, the number of T regulatory cell was higher in lung adenocarcinoma with pelp1 high-expression and pelp1 expression was negatively correlated with CD274 (PDL-1) and CTLA4. Therefore, PELP1 plays an important role in the malignant behavior of NSCLC and could be a potential therapeutic target. [ABSTRACT FROM AUTHOR]