Screening an Irish cohort with colorectal cancer for Lynch Syndrome using immunohistochemistry for mismatch repair proteins

Abstract

10547 Background: Large-scale screening for germ-line mutations that lead to the onset of disease in adulthood is possible owing to recent technical advances. The care of those with inherited predisposition to breast and ovarian cancer is now becoming a mainstream component of medical care. It is more difficult to identify those with Lynch Syndrome (LS) as various criteria (Amsterdam and Bethesda) have not proved definitive. An important development is the examination of tumor tissue to detect mismatch repair (MMR) protein loss using immunohistochemical (IHC) techniques. When coupled with family history those at risk of harbouring a mutation for LS can be identified. Once a mutation is identified predictive testing can be offered to family members, risk-reduction measures applied and mortality from colorectal cancer reduced. Methods: Screening for MMR protein expression (MLH1, MSH2, MSH6, PMS2) was planned on all colorectal cancer (CRC) cases using IHC on formalin-fixed tumor tissue from January 1st 2002. Local ethics committee approval was obtained and then written informed-consent from patients. Family history data was gathered from the index case or an appropriate relative. An aliquot of blood was stored from index cases for subsequent genetic screening if indicated by IHC analysis and genetic counseling. Results: 108 cases with CRC (62 male, 46 female, median age 59 years) from a potential total of 612 have been screened for MMR protein expression by a gastrointestinal pathologist and independently validated. Turn-around time for IHC analysis was 9 weeks. 5 patients (4.6%) had loss of MMR proteins, MSH2/MSH6- 2 cases, MSH6 alone- 1 case and MLH1/PMS2- 2 cases. All 5 have opted for genetic counselling and sequencing of relevant genes. Conclusion: These early results in an Irish cohort with CRC showing MMR loss in 4–5% of cases is consistent with other population findings. Microsatellite instability analysis is difficult, expensive and relatively unavailable. IHC, however, is an established technique in pathology departments and can be the cheapest and most reproducible approach to identify LS cases. IHC results along with robust family data can guide the genetic counseling process towards preventing deaths from CRC and other LS-associated cancers. No significant financial relationships to disclose.