Effect of tumor burden on survival in patients with stage IV EGFR-mutant NSCLC receiving osimertinib monotherapy.

8611 Background: Osimertinib (osi) has traditionally been given as monotherapy for patients (pts) with stage IV EGFR-mutant (EGFRm) non-small cell lung cancer (NSCLC), although acquired resistance remains a challenge. Recent data from the FLAURA2 study demonstrated a progression free survival (PFS) benefit of approximately 9 months (mos) when osi is combined with platinum-pemetrexed chemotherapy. Despite this improvement, combination therapy is associated with higher rates of adverse events, making it challenging to decide which pts should receive TKI + chemo vs TKI monotherapy. Tumor burden (TB) in pts with stage IV EGFRm NSCLC, which may be associated with risk of developing resistant clones on TKI monotherapy, and its association with clinical outcomes has not been examined. Methods: Retrospective, single institution manual case review of pts who received osi monotherapy. Primary objectives were PFS (i.e., oligoprogression requiring local therapy, disease progression (PD) with osi discontinuation, or death) and overall survival (OS) related to extent of TB. Those who did not receive osi monotherapy for stage IV EGFRm NSCLC or discontinued osi for reasons other than PD were excluded. Demographics, comorbidities, performance status, PD-L1 expression, histology, EGFRm subtype, prior TKI use, total number of visceral tumors (TTn), and total number/sites of metastatic disease (MDn) collected for analysis. Extent of TB categorized by TTn (1-4, 5-9, ≥10) and MDn (1-2, 3-4, ≥5). PFS and OS estimated by Kaplan-Meier method and compared using log-rank test. Results: 325 pts eligible for analysis. Median follow-up time was 22.7 mos. Median PFS (mPFS) for the overall cohort was 16.3 mos (95% CI; 13.7 - 18.9) and median OS (mOS) was 31.1 mos (95% CI; 27.4 - 39.3). Pts with a TTn of 1-4 had significantly better mPFS compared to those with a TTn of 5-9 and ≥10 (mPFS: 21.5 vs 16.3 vs 13.4 mos, respectively; P = 0.001). Pts with a TTn ≥10 had significantly worse mOS compared to those with a TTn of 5-9 and 1-4 (23.7 vs 35.1 vs 57.7 mos, respectively; P < 0.0001). Similarly, pts with a MDn of 1-2 had significantly better mPFS and mOS compared to those with a MDn of 3-4 and ≥5 (mPFS: 21.6 vs 11.4 vs 9.0 mos, respectively [P < 0.0001]; mOS: 44.3 vs 20.8 vs 22.4, respectively [P < 0.0001]). Pts with liver and bone mets had significantly worse mPFS and mOS, whereas those with lung and brain mets had worse mOS without affecting PFS. Conclusions: The extent of baseline TB, categorized by TTn and MDn, impacts both PFS and OS in pts with stage IV EGFRm NSCLC treated with osi monotherapy. Pts with “low-TB” (i.e., TTn 1-4, MDn 1-2) appear to have a survival advantage compared to those with “intermediate- or high-TB” (i.e., TTn 5-9 and ≥10, MDn 3-4 and ≥5) and may derive less benefit from the addition of chemotherapy to osi. Prospective, matched real-world treatment cohorts are warranted to optimize treatment strategies for this patient population.