Quantitative cell-free DNA, KRAS, and BRAF mutations in plasma from patients with metastatic colorectal cancer during treatment with cetuximab and irinotecan

Clin Cancer Res. 2012 Feb 15;18(4):1177-85. doi: 10.1158/1078-0432.CCR-11-0564. Epub 2012 Jan 6.


Purpose: The present study investigated the levels of circulating cell-free DNA (cfDNA) in plasma from patients with metastatic colorectal cancer (mCRC) in relation to third-line treatment with cetuximab and irinotecan and the quantitative relationship of cfDNA with tumor-specific mutations in plasma.

Experimental design: Inclusion criteria were histopathologically verified chemotherapy-resistant mCRC, adequate Eastern Cooperative Oncology Group performance status, and organ function. Treatment consisted of irinotecan being administered at 350 mg/m(2) for 3 weeks and weekly administration of 250 mg/m(2) cetuximab until progression or unacceptable toxicity. A quantitative PCR method was developed to assess the number of cfDNA alleles and KRAS and BRAF mutation alleles in plasma at baseline.

Results: The study included 108 patients. Only three patients were positive for BRAF mutations. The majority of KRAS mutations detected in tumors were also found in the plasma [32 of 41 (78%)]. Plasma cfDNA and plasma mutant KRAS levels (pmKRAS) were strongly correlated (r = 0.85, P < 10(-4)). The disease control rate was 77% in patients with low cfDNA (<25% quartile) and 30% in patients with high cfDNA [>75% quartile (P = 0.009)]. Patients with pmKRAS levels higher than 75% had a disease control rate of 0% compared with 42% in patients with lower pmKRAS (P = 0.048). Cox analysis confirmed the prognostic importance of both cfDNA and pmKRAS. High levels were clear indicators of a poor outcome.

Conclusions: KRAS analysis in plasma is a viable alternative to tissue analysis. Quantitative levels of cfDNA and pmKRAS are strongly correlated and hold promise of clinical application.

MeSH terms

  • Adult
  • Aged
  • Aged, 80 and over
  • Alleles
  • Antibodies, Monoclonal / administration & dosage
  • Antibodies, Monoclonal, Humanized
  • Antineoplastic Combined Chemotherapy Protocols / therapeutic use*
  • Camptothecin / administration & dosage
  • Camptothecin / analogs & derivatives
  • Cetuximab
  • Colorectal Neoplasms / diagnosis*
  • Colorectal Neoplasms / drug therapy*
  • Colorectal Neoplasms / mortality
  • DNA, Neoplasm / blood*
  • Female
  • Humans
  • Irinotecan
  • Male
  • Middle Aged
  • Mutation*
  • Neoplasm Metastasis
  • Prognosis
  • Proto-Oncogene Proteins / genetics*
  • Proto-Oncogene Proteins B-raf / genetics*
  • Proto-Oncogene Proteins p21(ras)
  • Treatment Outcome
  • ras Proteins / genetics*


  • Antibodies, Monoclonal
  • Antibodies, Monoclonal, Humanized
  • DNA, Neoplasm
  • KRAS protein, human
  • Proto-Oncogene Proteins
  • Irinotecan
  • BRAF protein, human
  • Proto-Oncogene Proteins B-raf
  • Proto-Oncogene Proteins p21(ras)
  • ras Proteins
  • Cetuximab
  • Camptothecin