Study patients and inclusion criteria

A total of 157 Japanese patients with interstitial pneumonia and lung cancer receiving treatment at the National Hospital Organization Osaka Toneyama Medical Center between January 2013 and December 2019 were screened. A patient inclusion flowchart is presented in Fig ​Fig1.1. Those patients who had secondary interstitial pneumonia were excluded. Usual interstitial pneumonia (UIP) was diagnosed based on the presence of a UIP pattern on high‐resolution computed tomography (CT) without surgical lung biopsy or specific combinations of high‐resolution CT findings and surgical lung biopsy patterns. ²⁴ Patients with small cell lung cancer, as well as those who did not undergo spirometry within one month after initiating chemotherapy, were excluded. Patients who had inoperable NSCLC due to recurrence or intolerability and/or disease progression were included. Moreover, only patients who started carboplatin‐based regimens as first‐line chemotherapy at least three days after the prescription of pirfenidone were included. One patient who discontinued pirfenidone before the initiation of chemotherapy for NSCLC was excluded. In total, 14 patients qualified for this study and were evaluated using examinations and analysis described in the following sections.

Patient inclusion flowchart. IP, interstitial pneumonia; IPF, idiopathic pulmonary fibrosis; NHO, National Hospital Organization; SCLC, small cell lung cancer.