Genetic modulation of the Let-7 microRNA binding to KRAS 3'-untranslated region and survival of metastatic colorectal cancer patients treated with salvage cetuximab-irinotecan

Pharmacogenomics J. 2010 Oct;10(5):458-64. doi: 10.1038/tpj.2010.9. Epub 2010 Feb 23.


There is increasing evidence that the Let-7 microRNA (miRNA) exerts an effect as a tumor suppressor by targeting the KRAS mRNA. The Let-7 complementary site (LCS6) T>G variant in the KRAS 3'-untranslated region weakens Let-7 binding. We analyzed whether the LCS6 variant may be clinically relevant to patients with metastatic colorectal cancer (MCRC) treated with anti-epidermal growth factor receptor (EGFR) therapy. LCS6 genotypes and KRAS/BRAF mutations were determined in the tumor DNA of 134 patients with MCRC who underwent salvage cetuximab-irinotecan therapy. There were 34 G-allele (T/G+G/G) carriers (25%) and 100 T/T genotype carriers (75%). G-allele carriers were significantly more frequent in the KRAS mutation group than in patients with KRAS wild type (P=0.004). In the 121 patients without BRAF V600E mutation, overall survival (OS) and progression-free survival (PFS) times were compared between carriers of the LCS6 G-allele genotypes and carriers of the wild-type T/T genotype. LCS6 G-allele carriers showed worse OS (P=0.001) and PFS (P=0.004) than T/T genotype carriers (confirmed in the multivariate model including the KRAS status). In the exploratory analysis of the 55 unresponsive patients with KRAS mutation, LCS6 G-allele carriers showed adverse OS and PFS times. These findings deserve additional investigations as they may open novel perspectives for the treatment of patients with MCRC.

Publication types

  • Clinical Trial
  • Research Support, Non-U.S. Gov't

MeSH terms

  • 3' Untranslated Regions*
  • Adult
  • Aged
  • Antibodies, Monoclonal / administration & dosage
  • Antibodies, Monoclonal / therapeutic use
  • Antibodies, Monoclonal, Humanized
  • Antineoplastic Combined Chemotherapy Protocols / administration & dosage
  • Antineoplastic Combined Chemotherapy Protocols / therapeutic use*
  • Camptothecin / administration & dosage
  • Camptothecin / analogs & derivatives
  • Camptothecin / therapeutic use
  • Cetuximab
  • Cohort Studies
  • Colorectal Neoplasms / drug therapy*
  • Colorectal Neoplasms / genetics
  • Colorectal Neoplasms / mortality
  • Colorectal Neoplasms / pathology
  • Disease-Free Survival
  • Female
  • Genotype
  • Humans
  • Irinotecan
  • Male
  • MicroRNAs / genetics*
  • Middle Aged
  • Neoplasm Metastasis
  • Proto-Oncogene Proteins / genetics*
  • Proto-Oncogene Proteins p21(ras)
  • Retrospective Studies
  • Salvage Therapy*
  • ras Proteins / genetics*


  • 3' Untranslated Regions
  • Antibodies, Monoclonal
  • Antibodies, Monoclonal, Humanized
  • KRAS protein, human
  • MicroRNAs
  • Proto-Oncogene Proteins
  • mirnlet7 microRNA, human
  • Irinotecan
  • Proto-Oncogene Proteins p21(ras)
  • ras Proteins
  • Cetuximab
  • Camptothecin