Predictive Impact of Diffuse Positivity for TTF-1 Expression in Patients Treated With Platinum-Doublet Chemotherapy Plus Immune Checkpoint Inhibitors for Advanced Nonsquamous NSCLC

Introduction: Pervious studies reported the association of TTF-1 expression with the efficacy of platinum-doublet chemotherapy in combination with immune checkpoint inhibitors in advanced nonsquamous NSCLC. Nevertheless, the predictive value of extent of TTF-1 expression (diffuse or focal TTF-1 positivity) remains unclear. Methods: The present study retrospectively reviewed 74 patients with TTF-1–positive recurrent or advanced nonsquamous NSCLC receiving first-line chemoimmunotherapy in a single institution in Japan. TTF-1 expression score in pretreatment tumor specimens was evaluated using immunohistochemistry, and the impact of chemoimmunotherapy response was analyzed. Results: In the total cohort, ≥50% of the tumor cells were TTF-1 positive (i.e., diffusely TTF-1 positive) in specimens of 61 patients (82.4%), whereas 10% to 49% of the tumor cells were TTF-1 positive (i.e., focally TTF-1 positive) in specimens of the remaining 13 patients (17.6%). In multivariate analysis, the median progression-free survival and overall survival (OS) were significantly longer in patients with diffusely TTF-1–positive tumors than in those with focally TTF-1–positive tumors (14.2 versus 9.2 mo, p = 0.01 and 30.2 versus 17.3 mo, p = 0.01, respectively). Moreover, the median OS was significantly longer in patients receiving chemoimmunotherapy including pemetrexed than in those receiving chemoimmunotherapy not including pemetrexed among the patients with diffusely TTF-1–positive tumors (not attained versus 23.2 mo, p < 0.01). Conclusions: The positive extent of diffuse TTF-1 expression associated with patient outcome was an independent predictive factor for better progression-free survival and OS in patients with advanced nonsquamous NSCLC receiving chemoimmunotherapy.