Patterns of immune checkpoint inhibitor utilization and PD-L1 testing in advanced gastroesophageal cancers using real-world data.

370 Background: Globally, gastroesophageal cancer (GEC) is a leading cause of morbidity and mortality, with poor 5-year overall survival (OS). The addition of immune checkpoint inhibitors (ICIs) such as nivolumab and pembrolizumab to chemotherapy has resulted in significant improvement in OS of those patients (pts) with metastatic GEC (mGEC), most notably in those with tumors exhibiting high PD-L1 CPS scores. However, the pattern of ICI utilization in associated PD-L1 testing since the adoption of this treatment (tx) has yet to be elucidated. We evaluated the patterns of ICI utilization and PD-L1/CPS testing in the first-line tx of mGEC pre and post FDA approval of ICI use in this setting. Methods: Pts ≥ 18 years of age, with recurrent/metastatic squamous or adenocarcinoma GEC diagnosed after 2011 were included from the de-identified nationwide Flatiron Health, electronic health record-derived database. We presented the proportion of pts receiving ICI therapy, stratified by line of tx, as well as the proportion of patients who received PD-L1 testing at 6-month intervals. Pts demographics and clinical characteristics, including age, gender, race, ECOG score, documented insurance, and stage at diagnosis (dx) were described and compared using T or Wilcoxon rank-sum tests for continuous variables, and chi-square or Fisher’s exact tests for categorical data. We compared tx rates and PDL-1 testing across four time points: time 1: Jan-June 2020, prior to ASCO data presentation; time 2: July-Dec 2020, ASCO data presentation; time 3: Jan- June 2021, FDA label change; time 4: July 2021 to 6 m after FDA label change using Chi-square test. Results: A total of 9,573 pts were included with 1,593 (16.6%) receiving ICI-based tx. Among these, 62.3% were White, 7% Black. Descriptive statistics indicated that pts with ICI- tx tend to be younger (median age 65y vs. 66.7; (p <0.001). Within the total cohort, 74% pt were dx before FDA approval of ICI tx, while 26% pts were dx after FDA approval. PD-L1 testing was conducted in 4,065 (42.5%) pts. A total of 1,268 (13%) pts received first-line ICI-based tx. Of these, 154 pts (12.1%) were treated before FDA approval, while 1,114 pts (87.9%) received tx following FDA approval. The rate of first-line ICI tx significantly increased at each subsequent time point Time 2: 11.2% (p <0.0001), Time 3: 32.9% (p <0.0001), Time 4: 37.4% (p <0.0001). PD-L1 testing rates also increased over time, particularly after FDA label change. Testing rates at Time 1 was 68%. Comparatively, testing rates at subsequent time points were: Time 2 (67.2%; p 0.88), Time 3 (71.5%; p 0.324) and Time 4 (77.4%; p=0.004). Conclusions: The approval of ICIs for first-line tx of mGEC led to a significant increase in both ICI utilization and PD-L1/CPS testing rates. Despite these advancements, ongoing disparities in tx access and testing highlight the need for further research and efforts to ensure equitable care.