Study population

After receiving institutional review board (IRB) approval at the University of Texas Southwestern Medical Center (UTSW), a retrospective analysis of deidentified reports was performed on a national cohort of 613 eligible patients who received ctDNA testing (Guardant360, Guardant Health) performed as part of routine clinical care. Eligibility criteria included a diagnosis of PDAC, CCA, EGC, or HCC, two ctDNA tests that were of the same versions between 1 October 2020 to 1 October 2021, and at least one detectable alteration on either the baseline or progression liquid biopsy. A subset of patients in this cohort (N = 35) had clinical and pathologic data accessible. Tissue specimens for these patients were identified only if they had been collected within 3 months of the baseline ctDNA collection and TMB analysis was determined from either targeted (FoundationOne) or exome sequencing (Caris Life Sciences). Tumor volumes were determined from radiographic images including computed tomography and magnetic resonance imaging performed within 4 weeks of liquid biopsies. To calculate tumor volumes, three-dimensional measurements (diameters on the axial, sagittal, and coronal plane) of all lesions for every lesion were used to calculate the volume of an ellipsoid (4/3 × π × width × length × height) which has been shown to approximate tumor volumes^48,49.

A separate cohort analysis was performed on patients who received cancer care between 1 August 2019 and 1 May 2022 for advanced PDAC, CCA, EGC, or HCC at UTSW and Parkland Hospital and had liquid biopsies analyzed using commercial assays including Guardant, Tempus, or Foundation as part of routine clinical care. Patients with at least two ctDNA tests that were of the same versions were identified and clinical data including demographics, treatment history, tumor responses, and survival outcomes were abstracted from the electronic medical record. This analysis was performed in accordance with Good Clinical Practices and the Declaration of Helsinki and approved by the UTSW IRB.