Background: Checkpoint inhibitors (CPI) targeting the PD1/PD-L1 axis significantly improved patient outcomes in stage IV non-small cell lung cancer (NSCLC). However, these patients will eventually develop resistance and progression. There is a need to identify novel treatment options. Poor response to PD-L1 antibody was correlated with increase in cancer-associated fibroblasts (CAF), which is known to interact with cytotoxic T cells (CTLs) by suppressing their function in a manner similar to regulatory T cells (Tregs). Production of cytokines by CAFs leads to impaired antitumor immunity by impairing CTL function (TGF beta) and prevent recruitment/mobilization of CTLs into tumors. These effects suggesting that CAF can be a therapeutic target in lung cancer resistant to checkpoint inhibitors. Pirfenidone (P) is approved to treat pulmonary fibrosis with anti-fibrotic effect by blocking the differentiation of fibroblasts into CAFs and suppress the production of TGF beta and TGF beta-induced signaling pathways/collagens. Atezolizumab is a humanized immunoglobulin (Ig) G1 monoclonal antibody that targets PD-L1 and inhibits the interaction between PD-L1 and its receptors, PD-1 and B7-1 (CD80), both of which function as inhibitory receptors expressed on T cells. We proposed a phase I/II trial to test the combination of atezolizumab (A) with P in patients with recurrent non-small cell lung cancer (NSCLC) after progression with CPI. The primary objective of phase I is to determine the maximum tolerated (MTD) dose of P in combination with A and assess the safety and tolerability of this combination. The secondary objective is to determine the efficacy of AP in all NSCLC participants treated in this study. Exploratory objectives include the measurement of circulating levels of TGF beta and research in expression of CAF related proteins. Methods: The initial phase I will enroll 3 patients using P at 801 mg po TID. A will be at 1200mg iv every 3 weeks. If there is ≤ 1 DLT, the study will proceed to phase II If there are 2- 3 DLT, P will be reduced to 534 mg TID. If there is ≤ 1 DLT, then this dose will proceed to phase II. If there is 2-3 DLT, then the study will be terminated. The phase II will enroll 16 patients to assess efficacy. Main inclusion criteria are patients with recurrent NSCLC after progression with first-line therapy CPI with or without chemotherapy, measurable disease, ECOG 0-2, and adequate organ function. Clinical trial information: NCT04467723