Detection and Quantitation of Circulating Tumor DNA KRAS Mutations from Patients with Unresectable Pancreatic Cancer
- A diagnostic and prognostic clinical tool with very high analytical sensitivity, clinical sensitivity, and quantitation is needed for therapeutic response monitoring.
- An estimated 90% of pancreatic cancers harbor somatic KRAS G12/G13 mutations.
- Recent studies on small numbers of patients demonstrate widely variable KRAS ctDNA sensitivity (27 – 71%)1.
- Accurate identification and quantitation of ctDNA KRAS mutation copies would be an improved prognostic and therapeutic response biomarker over CA19-9 which is known to be uninformative in 5-10% of patients with pancreatic cancer.
Study Design and Objectives
- Examine KRAS G12/13 detection rate in plasma of patients with unresectable, locally advanced or metastatic pancreatic cancer.
- Examine association between baseline KRAS levels in plasma and patient outcomes.
- Examine correlation between changes in KRAS levels in plasma and changes in tumor size by radiographic assessment following treatment with chemotherapy.
- Pretreatment (baseline) and longitudinal blood samples (1 – 4 mL) were prospectively collected from patients with unresectable pancreatic cancer through the Danish BIOPAC study (Figure 1; Table 1).
- ctDNA KRAS G12A/C/D/R/S/V, and G13D mutations were PCR enriched, sequenced by next generation sequencing (NGS), quantitated, and standardized.
- Standard curves were generated from a sample set with known numbers of spike-in copies for mutant KRAS molecules which were assayed in parallel with patient samples starting with PCR enrichment of mutant KRAS DNA followed by NGS.
- The number of mutant copies detected was standardized by normalizing the number of copies detected in the sample to a constant number of calculated genome equivalents (GEqs) of wild type DNA across all samples evaluated.
Highlighted Tables and Graphs
KRAS Status by Cancer Presentation
Concordance between KRAS mutation status and CA19-9
KRAS Mutation Corresponds with Response
- This is the largest, prospective dataset exploring ctDNA KRAS in unresectable pancreatic cancer.
- 92.9% of 210 patients with unresectable pancreatic cancer were positive for ctDNA KRAS.
- This detection rate closely matches the published prevalence of KRAS in pancreatic cancer (90%), and out performs previous studies, demonstrating the superior assay sensitivity.
- ctDNA analysis offers a viable tissue biopsy alternative for determining KRAS mutation status, especially in late stage patients.
- ctDNA KRAS analysis identified 52% more patients as positive than CA19-9, demonstrating KRAS as an improved diagnostic tool.
- Individuals with metastatic disease had a 8.2 fold difference in median ctDNA KRAS mutation load at baseline versus a 3.9 fold difference in baseline CA19-9. KRAS may represent an improved biomarker for metastatic disease over CA19-9.
- In two representative patients, dynamic changes in KRAS mutation load were consistent with response by imaging and predicted progressive disease months in advance of progression by imaging.
- Quantitation of KRAS mutant copy load may provide a more informative biomarker for prognosis and monitoring for therapeutic response.