A let-7 microRNA-binding site polymorphism in 3'-untranslated region of KRAS gene predicts response in wild-type KRAS patients with metastatic colorectal cancer treated with cetuximab monotherapy

Ann Oncol. 2011 Jan;22(1):104-109. doi: 10.1093/annonc/mdq315. Epub 2010 Jul 5.


Purpose: recent studies have found that KRAS mutations predict resistance to monoclonal antibodies targeting the epidermal growth factor receptor in metastatic colorectal cancer (mCRC). A polymorphism in a let-7 microRNA complementary site (lcs6) in the KRAS 3' untranslated region (UTR) is associated with an increased cancer risk in non-small-cell lung cancer and reduced overall survival (OS) in oral cancers. We tested the hypothesis whether this polymorphism may be associated with clinical outcome in KRAS wild-type (KRASwt) mCRC patients treated with cetuximab monotherapy.

Patients and methods: the presence of KRAS let-7 lcs6 polymorphism was evaluated in 130 mCRC patients who were enrolled in a phase II study of cetuximab monotherapy (IMCL-0144). Genomic DNA was extracted from dissected formalin-fixed paraffin-embedded tumor tissue, KRAS mutation status and polymorphism were assessed using direct sequencing and PCR restriction fragment length polymorphism technique.

Results: KRAS let-7 lcs6 polymorphism was found to be related to object response rate (ORR) in mCRC patients whose tumors had KRASwt. The 12 KRASwt patients harboring at least a variant G allele (TG or GG) had a 42% ORR compared with a 9% ORR in 55 KRASwt patients with let-7 lcs6 TT genotype (P = 0.02, Fisher's exact test). KRASwt patients with TG/GG genotypes had trend of longer median progression-free survival (3.9 versus 1.3 months) and OS (10.7 versus 6.4 months) compared to those with TT genotypes.

Conclusions: these results are the first to indicate that the KRAS 3'UTR polymorphism may predict for cetuximab responsiveness in KRASwt mCRC patients, which warrants validation in other clinical trials.

Publication types

  • Clinical Trial, Phase II

MeSH terms

  • 3' Untranslated Regions*
  • Adult
  • Aged
  • Aged, 80 and over
  • Antibodies, Monoclonal / therapeutic use*
  • Antibodies, Monoclonal, Humanized
  • Antineoplastic Agents / therapeutic use*
  • Binding Sites
  • Cetuximab
  • Colorectal Neoplasms / drug therapy*
  • Colorectal Neoplasms / genetics*
  • Female
  • Genes, ras*
  • Humans
  • Male
  • MicroRNAs / genetics*
  • Middle Aged
  • Mutation
  • Polymorphism, Genetic


  • 3' Untranslated Regions
  • Antibodies, Monoclonal
  • Antibodies, Monoclonal, Humanized
  • Antineoplastic Agents
  • MicroRNAs
  • mirnlet7 microRNA, human
  • Cetuximab