OBJECTIVES: Studies show that PD-L1 receptor expression is an independent survival prognosticator in gastric cancer patients. However, sparce real-world data exist on PD-L1 expression and decisions regarding treatment in gastric cancer. The objectives of this study were to assess PD-L1 expression and use of immune checkpoint inhibitor (ICI) therapies among gastric cancer patients in the U.S.

METHODS: This retrospective, observational study utilized de-identified data from five Cancer Treatment Centers of America (CTCA). Adults (≥ 18 years) diagnosed with gastric or gastroesophageal junction cancer and receiving treatment between 2016-2018 who also had PD-L1 testing at CTCA between 2016-2020 were included. Patients were followed until 12/31/2020 to identify timing and rate of ICI treatment.

RESULTS: Among 59 patients, 40 (68%) were male, average age was 55 years (SD=10.6), and 37 (62%) were metastatic at diagnosis. The average time from CTCA admission to PD-L1 test was 241 days (SD=320.5) and average time from diagnosis to PD-L1 test was 271 days (SD=318.8). Nineteen (32%) patients received an ICI 141 days (SD = 171.0) after testing, mostly (41%) in 3^rd line of therapy. The most commonly-prescribed ICI was pembrolizumab (96%). Thirteen (22%) patients had no PD-L1 tumor expression, 41 (68%) had 1-49% tumor expression, and 4 (7%) had ≥50% tumor expression at time of test; (1 test was inconclusive).

CONCLUSIONS: This study serves as a baseline comparator to trending real-world PD-L1 testing and ICI treatment in gastric cancer over time. Results demonstrated that while 75% of tested patients had PD-L1 expression, only 32% received an ICI. Future studies are warranted to understand whether rates and timing of PD-L1 testing have changed with availability of new ICIs and clinical guideline recommendations.