Abstract 765: Real-world serum CA19-9 level monitoring patterns and its association with clinical outcomes among patients with metastatic pancreatic ductal adenocarcinoma (mPDAC)

Background: Pancreatic cancer is expected to be the third deadliest cancer in the US in 2020. Evaluation of treatment response in patients (pts) with mPDAC necessitates scheduled clinical and radiographic assessments along with monitoring serum CA 19-9 levels. Currently available single-institution data examining the importance of CA 19-9 monitoring cannot be generalized to real-world settings. We investigated the impact of serum CA19-9 monitoring and its association with clinical outcomes in pts with mPDAC in a population-based setting. Methods: Data were extracted from the nationwide Flatiron Health electronic health record (EHR)-derived de-identified database for pts diagnosed with mPDAC between January 1, 2014 and June 30, 2020. Serum CA19-9 levels at baseline – defined as the values obtained ≤ 60 days 1L initiation and during first-line (1L) treatment were extracted. CA 19-9 levels > 40 IU/mL were considered elevated. Data regarding patient exposure to second (2L) and third-line (3L) systemic therapies were collected. Survival analysis was performed using Kaplan-Meier methods. Categorical measures were compared with the chi-square test and survival outcomes with the log-rank test. Results: Among the 6,118 pts identified, median age at treatment initiation was 68 years (IQR: 61 – 75), 55% were male, 67% were white, and 73% had a baseline serum CA 19-9 level available. Among 4,486 pts with baseline CA 19-9 levels available, 701 (15%) had a normal (< 40 U/mL) level. Among 3,867 pts with elevated CA 19-9 at baseline, 534 (14%) had a single 1L assay and 2,448 (63%) had > 1 assay during 1L treatment. The proportions of pts who received 2L/3L treatment were 25%/7.6% among pts with no CA 19-9 assays performed at any time, 14%/3.7% among pts with only baseline CA 19-9 assays, 31%/9.7% among pts with a single CA 19-9 assay during 1L treatment (with or without a baseline assay), and 50%/17% if they had more than one CA 19-9 assay performed during the course of their 1L treatment (p < 0.001). Median OS (mOS) for pts who had no baseline serum CA 19-9 measurement, a normal baseline CA 19-9 level or an elevated baseline CA 19-9 level were 6.3 months, 8.8 months and 7.2 months, respectively (p < 0.001). The mOS of pts with no baseline CA 19-9 assay, only baseline assays, a single assay during 1L and > 1 assay during 1L was 3.8, 1.9, 4.2, and 11 months, respectively (p < 0.001). Conclusions: In one of the largest, contemporary, real-world studies of patients with mPDAC to date, elevated CA 19-9 level at diagnosis demonstrated a prognostic impact. Routine serial monitoring of CA 19-9 levels during 1L treatment may be warranted, in addition to clinical and radiographic assessment, and may translate into better patient outcomes. Further validation studies are needed to understand the generalizability of these results. Citation Format: Ben George, Matthew Kent, Andy Surinach, Neil Lamarre, Paul Cockrum, Aleksander Chudnovsky. Real-world serum CA19-9 level monitoring patterns and its association with clinical outcomes among patients with metastatic pancreatic ductal adenocarcinoma (mPDAC) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 765.