Bethesda guidelines: relation to microsatellite instability and MLH1 promoter methylation in patients with colorectal cancer

Ann Intern Med. 2001 Oct 16;135(8 Pt 1):566-76. doi: 10.7326/0003-4819-135-8_part_1-200110160-00007.


Background: Microsatellite instability is a hallmark of mismatch repair deficiency in hereditary nonpolyposis colorectal cancer and results from mutations in the mismatch repair genes MLH1 or MSH2 or from gene inactivation associated with DNA methylation. The Bethesda guidelines were established to identify patients with colorectal cancer who should be tested for microsatellite instability.

Objective: To assess the Bethesda guidelines for detection of microsatellite instability and to determine the role of MLH1 promoter methylation in colorectal cancer.

Design: Prospective cohort study.

Setting: Tertiary care referral center in Frankfurt, Germany.

Patients: 125 consecutive patients with colorectal cancer.

Measurements: Patients were assessed according to the Bethesda guidelines, and tumor specimens were analyzed for microsatellite instability. Patients with microsatellite instability were tested for MLH1 promoter methylation and MLH1 and MSH2 germline mutations.

Results: Microsatellite instability was detected in 17 of 58 patients who fulfilled and 5 of 67 patients who did not fulfill criteria of the Bethesda guidelines. In 11 of 17 patients with microsatellite instability who fulfilled Bethesda guidelines, an MLH1 (n = 3), MSH2 (n = 7), or combined MLH1 and MSH2 (n = 1) mutation was found. Among the patients with microsatellite instability who did not fulfill Bethesda guidelines, no mutations were observed; MLH1 promoter methylation was observed in 6 of 11 patients with an MLH1 or MSH2 mutation and 5 of 11 patients without an MLH1 or MSH2 mutation.

Conclusions: The Bethesda guidelines are useful for selecting patients for microsatellite instability testing. MLH1 and MSH2 testing should be recommended in all patients with colorectal cancer and microsatellite instability who fulfill at least one Bethesda criterion. MLH1 promoter methylation may accompany rather than initiate carcinogenesis in patients with colorectal cancer who have mismatch repair gene defects.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptor Proteins, Signal Transducing
  • Adult
  • Aged
  • Aged, 80 and over
  • Base Pair Mismatch*
  • Carrier Proteins
  • Colorectal Neoplasms, Hereditary Nonpolyposis / genetics*
  • DNA Methylation*
  • DNA Repair
  • DNA-Binding Proteins*
  • Female
  • Germ-Line Mutation
  • Humans
  • Male
  • Microsatellite Repeats / genetics*
  • Middle Aged
  • MutL Protein Homolog 1
  • MutS Homolog 2 Protein
  • Neoplasm Proteins / genetics*
  • Neoplasm Proteins / metabolism
  • Nuclear Proteins
  • Practice Guidelines as Topic*
  • Promoter Regions, Genetic / genetics
  • Prospective Studies
  • Proto-Oncogene Proteins / genetics
  • Proto-Oncogene Proteins / metabolism


  • Adaptor Proteins, Signal Transducing
  • Carrier Proteins
  • DNA-Binding Proteins
  • MLH1 protein, human
  • Neoplasm Proteins
  • Nuclear Proteins
  • Proto-Oncogene Proteins
  • MSH2 protein, human
  • MutL Protein Homolog 1
  • MutS Homolog 2 Protein