Discontinuation of immunotherapy over 2 years for patients with non-small cell lung cancer (NSCLC): A search for predictors

2661 Background: In advanced NSCLC, treatment completion at 24 months emerged in trials evaluating immune checkpoint inhibitors (ICI). Nevertheless, in clinical practice the question of the optimal treatment duration is under debate. Methods: We performed a retrospective study on advanced NSCLC treated with ICI (alone or with chemotherapy) at Gustave Roussy before 2021. Among patients still receiving ICI at 12 months, we analyzed the reasons for ICI discontinuation at 18 and 24 months. Results: Of the 682 patients treated with ICI (first-line for n=230, 33.7%), 159 (23.3%) received ICI for ≥ 12 months and 122 (17.9%) for ≥ 18 months. Between 18-24 months, 20 (57.1%) patients interrupted ICI for progressive disease (PD), 8 (22.8%) for toxicity and 7 (20.0%) after discussion with the patient. Out of the 88 (12.9%) patients who completed 2-years of ICI (median duration of treatment: 31.46 months, first-line for n=51), 22 (25.0%) patients discontinued ICI for PD and 40 (45.5%) without PD: 14 (15.9%) for toxicities, patient request or unknown causes and 26 (29.5%) for clinical decision before (n=16, 61.5%) or after (n=10, 38.5%) 30 months of treatment. Discontinuation according to phase III clinical trial design was supported by complete response (CR) by PET imaging +/- tissue biopsy of metabolically active lesions +/- ctDNA in 17 (65.4%) cases just before therapy discontinuation. After a median follow-up of 45.6 months since treatment discontinuation for these 26 patients, only two experienced PD at 4 and 6 months from ICI interruption, in both cases with no proof of CR at ICI discontinuation (p=0.111). The remaining 26 (29.5%) patients who continued ICI after 2 years, are on treatment based either on absence of CR at PET-CT +/- tissue biopsy of metabolically active lesions (n=20, 76.9%) or after discussion with the patients (n=6, 23.1%). After a median follow-up of 40.17 months from the of 24-months landmark, the median progression-free survival was unreached in both continuation and discontinuation groups. Conclusions: The patients who completed 2-years of ICI treatment usually continue to experience long‐term response after discontinuation. Considering that a subgroup of patients could still benefit from maintained ICI administration, PET imaging was considered to guide ICI cessation or continuation. Prospective studies specifically designed to investigate biomarkers of maintained responses or residual disease (imaging, ctDNA, multi-omics including microbiome) are required to establish the indication for ICI continuation or stop for each patient.