Background: Clinical trial (CT) IMpower133 met both primary endpoints and is the first CT to show significant clinical improvement over standard chemotherapy (C) with a good safety profile in first line (1L) ES-SCLC. The addition of ATZ to CB + ET resulted in an OS landmark of 34% and 22% compared to 21% and 16.8% of patients alive at 18 and 24 months respectively versus C. IMfirst evaluates ATZ + CB or CP + ET in a broader patient population than the pivotal study. ECOG Performance status (PS) 2, asymptomatic untreated brain metastases, underlying stable autoimmune diseases and HIV+ pts are eligible. IMfirst also includes the possibility of 6 C induction cycles according to investigator´s choice and consolidation radiotherapy. Methods: To evaluate the safety and efficacy of ATZ added to CB or CP + ET as 1L treatment in an interventional real world setting of ES-SCLC. Exploratory endpoints include tumor biomarker analysis related to ATZ. Results: As of Oct 2020, 117 pts had been enrolled, 105 treated with ATZ + CB + ET and 12 with ATZ + CP + ET. The median age was 65 years (Y) (range 35-89); 84 males; 14 pts (12%) had CNS metastases and 66 pts were current smokers and 50 former smokers, one had never smoked. The PS was 0 in 28 pts (24%), 1 in 75 (64%) and 2 in 14 (12%). The median of cycles of ATZ received was 4 for all the pts (range 1-12) and 2 for the pts (40) in maintenance phase (range 1-8). Number of pts with adverse events (AEs) was 109, 36 with Serious Adverse Events (SAEs) and 63 with AEs. 8 pts had SAEs related to treatment, 4 had adverse events of special interest and 13 pts discontinued the treatment due to AEs: 6 to ATZ, 12 to CB or CP and 10 to ET, 1 patient discontinued ATZ due to a related AE. Table shows the treatment related AEs (TRAEs). No grade 5 TRAEs were reported. Conclusions: IMfirst induction phase analysis confirms the safety profile of ATZ plus C in a broader population of patients. Efficacy, biomarker and further safety analyses will be presented in the future with longer follow up.

Regarding the immune-mediated AEs (IMAEs), there were two pts (2.6%) with grade 1 and 2 hyperthyroidism. One patient had a grade 2 increase in Alanine Aminotransferase. One patient presented grade 4 hepatotoxicity and another one had grade 3 pneumonitis. All patients with IMAEs were treated accordingly.