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Objective To investigate the response characteristics of patients with locally advanced/metastatic non-squamous non-small cell lung cancer (nsq-NSCLC) treated with tislelizumab in combination with chemotherapy in the first line. Methods Patients with nsq-NSCLC who achieved complete or partial remission after treatment with tislelizumab in combination with chemotherapy or chemotherapy alone in the RATIONALE 304 study, as assessed by an independent review board, were selected to analyze the response characteristics and safety profile of the responders. Time to response (TTR) was defined as the time from randomization to the achievement of first objective response. Depth of response (DpR) was defined as the maximum percentage of tumor shrinkage compared with the sum of the baseline target lesion length diameters. Results As of January 23, 2020, 128 patients treated with tislelizumab in combination with chemotherapy achieved objective tumor response (responders), representing 57.4%(128/223) of the intention-to-treat population, with a TTR of 5.1 to 33.3 weeks and a median TTR of 7.9 weeks. Of the responders (128), 50.8%(65) achieved first remission at the first efficacy assessment (week 6), 31.3%(40) at the second efficacy assessment (week 12), and 18.0%(23) at the third and subsequent tumor assessments. The percentages of responders who achieved a depth of tumor response of 30% to <50%, 50% to <70% and 70% to 100% were 45.3%(58/128), 28.1%(36/128) and 26.6%(34/128), respectively, with median progression-free survival (PFS) of 9.0 months (95% CI: 7.7 to 9.9 months), 11.5 months (95% CI: 7.7 months to not reached) and not reached (95% CI: 11.8 months to not estimable), respectively. Tislelizumab plus chemotherapy were generally well tolerated in responders with similar safety profile to the overall safety population. Conclusion Among responders to tislelizumab in combination with chemotherapy for nsq-NSCLC, 82.0%(105/128) achieves response within the first two tumor assessments (12 weeks) and 18.0%(23/128) achieves response at later (18 to 33 weeks) assessments, and there is a trend toward prolonged PFS in responders with deeper tumor response. [ABSTRACT FROM AUTHOR]