PDCD1 and squamous cell carcinoma: Studies have reported that the incidence of CIP is more often associated with smoking history (47), age over 70 years (38), squamous cell carcinoma subtype(> adenocarcinoma subtype) (31, 48, 49), combination therapy (> ICI monotherapy) (50, 51), PD-1 inhibitors (> PD-L1 and CTLA-4 inhibitors) (51, 52), the presence of baseline fibrosis on chest CT scans (11, 53), and pre-existing pulmonary diseases including IPF, ILDs, chronic obstructive pulmonary disease (COPD), and asthma (14, 13, 54).