Background: Thyroid transcription factor-1 (TTF-1) expression in advanced non-squamous non-small cell lung cancer (NSCLC) has been associated with the efficacy of pemetrexed plus platinum chemotherapy. However, the relation between TTF-1 expression and efficacy of the combination of programmed cell death 1 (PD-1)/programmed cell death ligand 1 (PD-L1) inhibitors plus pemetrexed and platinum chemotherapy, a standard first-line treatment regimen for advanced non-squamous NSCLC, has remained unclear. Methods: We retrospectively evaluated TTF-1 expression in tumor tissue of patients with advanced or recurrent non-squamous NSCLC treated with PD-1/PD-L1 inhibitors plus pemetrexed and platinum chemotherapy in the first-line setting. Clinical characteristics and pathological data for each patient were assessed, and progression-free survival (PFS) was evaluated. Bias due to patient background was minimized by application of inverse probability of treatment weighting (IPTW) analysis. Results: A total of 122 patients, 75 (61.5%) of whom were positive for TTF-1 immunostaining in tumor specimens, was included in this multicenter study. At the time of analysis, 89 (73.0%) patients had experienced progression events and 44 (36.1%) had died [median follow-up 14.6 months (range, 0.53–29.5 months)]. PFS was longer for TTF-1-positive patients than for TTF-1-negative patients [median, 12.2 vs. 6.0 months; hazard ratio (HR) =0.63 (95% CI: 0.37–1.06); log-rank P=0.028]. IPTW-adjusted PFS was significantly longer for TTF-1-positive than for TTF-1–negative patients [HR =0.62 (95% CI: 0.46–0.83); log-rank P=0.024]. Conclusions: TTF-1 expression in advanced non-squamous NSCLC can serve as a basis for prediction of PFS in patients treated with PD-1/PD-L1 inhibitors plus pemetrexed and platinum chemotherapy in the first-line setting.
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