title: Microsatellite instability analysis and/or immunostaining for the diagnosis of hereditary nonpolyposis colorectal cancer?
abstract: Hereditary nonpolyposis colorectal cancer (HNPCC) represents 2-4% of colorectal cancers and is caused by a constitutional defect in a mismatch repair (MMR) gene, most commonly affecting the genes MLH1, MSH2, and MSH6. The MMR defect results in an increased cancer risk with the greatest lifetime risks for colorectal cancer and endometrial cancer. The HNPCC-associated tumor phenotype is generally characterized by microsatellite instability (MSI) and immunohistochemical loss of expression of the affected MMR protein. We have evaluated the information obtained from MSI analysis and immunostaining for MLH1, MSH2, and MSH6 in a series of 128 tumors from patients suspected of having HNPCC. A MSI-high pattern was present in 59 of 128 (46%) tumors. Loss of immunohistochemical expression for at least one of these MMR proteins was found in 54 of 59 (92%) evaluable MSI tumors. This loss affected MLH1 in 28, MSH2 in 22, and MSH6 in 21 tumors (with MSH6 as the only loss in 4 tumors). Five (8%) MSI-high tumors showed normal MMR protein expression. All 69 microsatellite stable or MSI-low tumors showed normal immunostaining for all three proteins. In 28 patients, all with MSI-H tumors, germ-line mutations of MLH1, MSH2, or MSH6 had been identified, and a corresponding immunohistochemical loss of MMR protein expression was identified in all these cases. In summary, immunostaining for the MMR proteins MLH1, MSH2, and MSH6 had a sensitivity of 92% and a specificity of 100% for detecting MMR-deficient tumors. MMR protein immunostaining facilitates mutation analysis in suspected HNPCC patients, since it pinpoints the mutated gene, but until the genetic background to the MSI tumors with retained MMR protein expression has been clarified, we suggest that MSI and MMR protein immunostaining should optimally be combined in clinical HNPCC analysis.
authors.affiliation: Department of Pathology, The Jubileum Institution, Lund University Hospital, 221 85, Lund, Sweden. Britta.Halvarsson@helsingborgslasarett.se
authors.forename: Britta
authors.initials: B
authors.lastname: Halvarsson
authors.forename: Annika
authors.initials: A
authors.lastname: Lindblom
authors.forename: Eva
authors.initials: E
authors.lastname: Rambech
authors.forename: Kristina
authors.initials: K
authors.lastname: Lagerstedt
authors.forename: Mef
authors.initials: M
authors.lastname: Nilbert
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D014408:Biomarkers, Tumor / Q000032:analysis*; D002352:Carrier Proteins; D003123:Colorectal Neoplasms, Hereditary Nonpolyposis / Q000175:diagnosis*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D005260:Female; D018095:Germ-Line Mutation; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D018895:Microsatellite Repeats; D008875:Middle Aged; D000070957:MutL Protein Homolog 1; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism; D009687:Nuclear Proteins; D016133:Polymerase Chain Reaction; D012680:Sensitivity and Specificity
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D014408:Biomarkers, Tumor; D002352:Carrier Proteins; D004268:DNA-Binding Proteins; C094443:G-T mismatch-binding protein; C501486:MLH1 protein, human; D009363:Neoplasm Proteins; D009687:Nuclear Proteins; D000070957:MutL Protein Homolog 1