The retinoblastoma gene (RB1) encodes the retinoblastoma (RB) pocket protein that plays an important role in cell cycle progression. Here we determine the frequency and prognostic significance of RB1 mutation in non small cell lung cancer (NSCLC), restricting inclusion to Stage III and IV patients with linked genomic and clinical data. The primary outcome was median overall survival (OS). We identified RB1 mutation in 8.2% of NSCLC patients. The median OS for wild‐type (wt) RB1 was 28.3 months vs 8.3 months for mutant RB1 (Hazard Ratio = 2.59, P = 0.002). Of special interest, RB1 mutation also correlated with lack of response to immunotherapy. Our study focused on RB1 mutation in locally advanced and advanced non small cell lung cancer to better facilitate comparisons with small cell lung cancer (SCLC). In our SCLC cohort, RB1 mutation was identified in 75% of patients and wt RB1 was associated with significantly shorter OS (P = 0.002). The different outcomes of RB1 mutation observed among lung cancer subtypes suggest a more complicated mechanism than simple regulation of cell cycle or response to chemotherapy.

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9034 Background: The addition of A to C+ Paclitaxel (Pac) + plus B improved progression free survival (PFS) and overall survival (OS) compared with C + Pac + B alone in pts with metastatic NS-NSCLC. However, C + Pem is more commonly used for this patient population with a shorter infusion time and favorable toxicity profile compared with Pac. Methods: Multicenter single arm phase II clinical trial of chemo and immunotherapy-naïve pts with stage IV NSq-NSCLC. All pts received A (1200 mg, D1) + C (AUC 5, D1) + P (500 mg/m2, D1) + B (15mg/kg D1) q3 week x4. If non-PD, pts could receive maintenance APB until PD or intolerable side effects. The primary endpoint was 1 yr. PFS. Sample size of 42 planned with 87% power and two-sided type I error of 0.05 for 1 yr PFS. Secondary endpoints included ORR, disease control rate (DCR) [defined by CR + PR + SD], and toxicity. Results: 30 pts were enrolled from 11/15/2018 to 10/5/2020. The study was closed early due to 3 patient deaths, possibly related to treatment (VTE, Febrile neutropenia, colonic perforation). Median age 64 (range 38-83); M/F 20/10; mutations in EGFR/ALK/KRAS/BRAF (5/1/4/2); PD-L1 TPS < 1%/1-49%/ > 50% (9/14/6) and one pt did not have PDL-1 status. Median f/u was11.6 mos (range 1-20). ORR 35.71% (95% CI: 18.64%-55.95%), DCR 92.85% (95% CI: 83%-100%). 1yr PFS and OS were 55.27% and 82.90% respectively. The most common G III and G II toxicity were HTN (20%) and fatigue (33.3%).3 pts had G IV toxicity (Anemia, Febrile neutropenia and colonic perforation) and 2 pts had Grade (G) V toxicity (VTE, Hypoxia/Sepsis). Conclusions: Atezolizumab + Carboplatin + Pemetrexed + Bevacizumab was associated with longer DCR, PFS, and OS than historical controls. 3 on-treatment deaths, possibly related to therapy (more likely bevacizumab), prompted early closure. A phase 3 study evaluating this regimen is ongoing by another group NCT03786692. Clinical trial information: NCT03713944.