Use of urinary circulating tumor DNA KRAS for monitoring treatment response in patients with metastatic colorectal cancer
Colorectal cancer (CRC) is the third cause of cancer mortality in the United States. Despite advances in early detection, each year more than 50,000 patients are diagnosed with metastatic disease. Combination chemotherapy, targeted drugs, and surgical interventions have revolutionized the treatment landscape and improved survival of these patients. Radiographic imaging in patients with mCRC is the current standard of care for monitoring responses. At least 40% of patients with mCRC have tumor-associated KRAS mutations, and these may be detected in tumor DNA in plasma and urine. The aim of this study was to correlate the dynamics of KRAS mutational load in urinary ctDNA with clinical responses in patients with mCRC.
ctDNA KRAS G12/13 assay (Figure 1)
- Urinary ctDNA was extracted using the Trovagene platform that preferentially isolates small fragmented DNA.
- A quantitative mutation enrichment PCR- next-generation sequencing assay detects all KRAS codon 12/13 variants.
- For greater sensitivity in fragmented ctDNA, the assay utilizes a 31bp footprint. A selective enrichment step for mutated DNA fragments suppresses wild-type (WT) sequence amplification with a blocker. Barcoded adaptor primers are added for compatibility with next-generation sequencing (MiSeq).
Highlighted Tables and Graphs
ctDNA KRAS G12/13 Assay Performance
Monitoring Molecular Response to Chemotherapy by Urinary KRAS
- ctDNA testing by urine and plasma has high sensitivity and detects KRAS mutations concordant with tumor biopsy.
- Dynamics of urinary ctDNA KRAS G12/13 mutational load correlated with clinical course in mCRC patients.
- Decrease in urine or plasma ctDNA KRAS G12/13 mutation levels after 2 weeks of chemotherapy detects molecular response in advance of radiographic response.
- In one patient (Patient 1), radiographic progression was detected 2-3 scan cycles after rising ctDNA KRAS mutation was observed in urine.