Pneumocystis jirovecii Pneumonia in Patients with Lung Cancer Receiving Immune Checkpoint Inhibitors: A Retrospective Nationwide Population-Based Cohort Study from South Korea

Background This study determined the incidence of Pneumocystis jirovecii pneumonia (PCP) in patients with lung cancer based on immune checkpoint inhibitor (ICI) exposure. Methods National claims data were obtained from 68,174 patients with lung cancer treated with ICIs or comparator non-ICIs (cytotoxic chemotherapy, targeted therapy, or both) between August 2017 and December 2021 in South Korea. The ICI exposure group included patients who were treated with ICIs at least once during the study period. The incidence and standardized incidence ratios were computed according to sex, 10-year age, and calendar-specific cancer population, to estimate the effects of ICIs and non-ICIs on the incidence of PCP. A logistic regression analysis was performed that adjusted for sex, age, comorbidities, and concomitant immunosuppressive drugs use. Results A total of 18,043 (26.4%) patients were in the ICI exposure group, and 50,131 (73.6%) were in the ICI non-exposure group. More than half of the patients in the ICI exposure group were men aged 60–79 years. Twenty-one PCP events occurred every 42,000.39 person-years in the ICI exposure group, and the incidence of PCP was lower than that in the ICI non-exposure group. Compared to the total cancer population, the incidence of PCP in patients with lung cancer was not significantly affected by ICI exposure, sex, or age. A 36% decreased risk of PCP with ICI exposure compared with non-exposure was estimated; however, this result was not statistically significant. Conclusions The incidence of PCP in patients with lung cancer treated with ICIs did not differ significantly from that in patients not treated with ICIs.