Brief report

Cancer Causes & Control

, Volume 20, Issue 9, pp 1763-1768

First online:

Microsatellite instability and survival in rectal cancer

  • Wade S. SamowitzAffiliated withDepartment of Pathology, University of Utah Health Sciences Center Email author 
  • , Karen CurtinAffiliated withDepartment of Internal Medicine, University of Utah Health Sciences Center
  • , Roger K. WolffAffiliated withDepartment of Internal Medicine, University of Utah Health Sciences Center
  • , Sheryl R. TrippAffiliated withDepartment of Pathology, University of Utah Health Sciences Center
  • , Bette J. CaanAffiliated withDivision of Research, Kaiser Permanente Medical Care Program
  • , Martha L. SlatteryAffiliated withDepartment of Internal Medicine, University of Utah Health Sciences Center

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Abstract

Objective

High levels of microsatellite instability (MSI-H) have been associated in many studies with improved prognosis in colon cancer. Very few studies have evaluated the effect of MSI-H on rectal cancer survival. We assessed MSI-H and other genetic and epigenetic changes on survival of 990 individuals diagnosed with first primary rectal cancer.

Methods

MSI was assessed primarily by instability in the mononucleotide repeat BAT-26. The BRAF V600E mutation was assessed by TaqMan assay. The CpG island methylator phenotype (CIMP) was determined by methylation-specific PCR of CpG islands in MLH1, methylated in tumors (MINT)1, (MINT)2, (MINT)31 and CDKN2A. KRAS2 codons 12 and 13 mutations, and TP53 mutations in exons 5–8 were determined by sequencing.

Results

Multivariate analysis revealed that MSI-H (HRR 2.47, 95% CI 1.13–5.40) and KRAS2 mutations (HRR 1.37, 95% CI 1.04–1.81) were associated with a significantly higher risk of dying of rectal cancer. Only one of 22 MSI-H tumors showed a BRAF V600E mutation. Of 15 MSI-H rectal cancers evaluated for methylation, two exhibited MLH1 methylation and four exhibited CIMP.

Conclusion

The genetic and epigenetic characteristics of MSI-H rectal cancers suggest that they are enriched for Lynch-associated tumors; adverse prognosis associated with MSI-H in these tumors may reflect the relatively high frequency of Lynch-associated cancers and/or the effect of radiation or chemotherapy on Lynch-associated rectal cancers or MSI tumors in general.

Keywords

Colorectal cancer Microsatellite instability Lynch syndrome Survival Hereditary nonpolyposis colorectal cancer