Is PET/CT Useful in Detecting Pneumocystis jirovecii Colonization in Patients with Primary Lung Cancer?

Background/Objectives:Pneumocystis jirovecii colonization induces persistent low-grade pulmonary inflammation, which may alter fluorodeoxyglucose (FDG) uptake in positron emission tomography/computed tomography (PET/CT). We aimed to evaluate whether asymptomatic infection influences the maximum standardized uptake value (SUVmax) or clinicopathological parameters of primary lung cancer. Methods: In this prospective single-center observational study, 107 consecutive patients undergoing surgical resection for primary lung cancer were enrolled. Preoperative FDG PET/CT scans were obtained within four weeks prior to surgery. Intraoperative respiratory secretions and lung tissue samples were analyzed for P. jirovecii, using nested polymerase chain reaction (nested-PCR) targeting the mitochondrial large subunit rRNA gene. Propensity score matching (PSM) adjusting for age, sex, and body mass index was performed across 1:1, 1:2, and 1:3 matching models. Results:Pneumocystis jirovecii colonization was confirmed in 12 of 107 patients (11.21%). In the unadjusted cohort, no significant differences in primary lesion SUVmax were identified between positive and negative patients (10.38 ± 6.50 vs. 8.86 ± 6.58, p = 0.411), nor across matched models (1:1: p = 0.555; 1:2: p = 0.951; 1:3: p = 0.926). Following PSM, patients without colonization exhibited significantly larger maximum tumor diameters in both 1:2 (30.71 ± 19.23 vs. 18.25 ± 6.63 mm, p = 0.035) and 1:3 matching models (29.08 ± 17.47 vs. 18.25 ± 6.63 mm, p = 0.035). Conclusions: We did not find any association between P. jirovecii colonization and preoperative metabolic tumor staging on FDG PET/CT. However, asymptomatic carriage was associated with smaller primary tumor dimensions following propensity adjustment in 1:2 and 1:3 matching models, warranting further exploration of host-fungal interactions within the pulmonary tumor microenvironment.