Impact of TTF-1 Expression on the Prognostic Prediction of Patients with Non–Small Cell Lung Cancer with PD-L1 Expression Levels of 1% to 49%, Treated with Chemotherapy vs. Chemoimmunotherapy: A Multicenter, Retrospective Study

Purpose Thyroid transcription factor 1 (TTF-1) expression is a useful predictor of treatment efficacy in advanced non-squamous non–small cell lung cancer (NSCLC). This study aimed to evaluate whether TTF-1 could predict the effectiveness of chemotherapy versus chemoimmunotherapy in patients with non-squamous NSCLC with programmed death ligand-1 (PD-L1) expression between 1% and 49%. Materials and Methods We conducted a retrospective study of patients with NSCLC who were treated with chemotherapy or chemoimmunotherapy between March 2016 and May 2023. The patients had histologically confirmed NSCLC, stage III-IV or postoperative recurrence, TTF-1 measurements, and PD-L1 expression levels between 1% and 49%. Clinical data were analyzed to evaluate the effect of TTF-1 expression on treatment efficacy. Results This study included 283 of 624 patients. TTF-1–positive patients showed longer progression-free survival (PFS) and overall survival (OS) (PFS: 6.4 months [95% confidence interval (CI), 5.0 to 9.4] vs. 4.1 months [95% CI, 2.7 to 6.1], p=0.03; OS: 17.9 months [95% CI, 15.2 to 28.1] vs. 9.4 months [95% CI, 6.3 to 17.0], p < 0.01) in the chemotherapy cohorts (n=93). In the chemoimmunotherapy cohort (n=190), there was no significant difference in PFS and OS between TTF-1–positive and –negative groups (PFS: 7.6 months [95% CI, 6.4 to 11.0] vs. 6.0 months [95% CI, 3.6 to 12.6], p=0.59; OS: 25.0 months [95% CI, 18.0 to 49.2] vs. 21.3 months [95% CI, 9.8 to 28.8], p=0.09). Conclusion In patients with NSCLC with PD-L1 expression between 1% and 49%, TTF-1 expression was a predictor of chemotherapeutic, but not chemoimmunotherapeutic, efficacy.