- 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.
- 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.