title: Detecting BRCA2 protein truncation in tissue biopsies to identify breast cancers that arise in BRCA2 gene mutation carriers.
abstract: OBJECTIVE
  Mutations in the BRCA2 gene are dominantly inherited but cause cancers when the wild-type allele has loss of heterozygosity (LOH) within the cancer. Because most disease-associated BRCA2 mutations are protein-truncating mutations, a test for truncated BRCA2 proteins should identify most BRCA2 hereditary cancers.
  
  
  METHODS
  We have developed a tissue truncation test to identify truncated BRCA2 proteins in breast cancer tissue biopsies in vivo that does not use amplification or genetic manipulations. N-terminal and C-terminal antibodies are used to visualize protein truncation by demonstrating that the beginning of the protein is present but the end (ie, terminus) is absent.
  
  
  RESULTS
  A quantitative C-terminal immunostaining score or a C-terminal to N-terminal truncation ratio correctly classified 20 of 21 breast cancers arising in BRCA2 mutation carriers and 57 of 58 cancers arising outside the context of a multiple-case breast cancer family. This represents a sensitivity of 95% and a specificity of 98%. Because of the presence of C-terminal BRCA2 protein and atypical clinical features of the misclassified cancer in a BRCA2 mutation carrier, we performed polymerase chain reaction and sequence analyses on this cancer. The results showed continued presence of the BRCA2 wild-type allele in the cancer, which indicated that intact BRCA2 protein was present in this cancer.
  
  
  CONCLUSIONS
  This immunohistochemistry-based test (which takes only 4 hours) appears to identify BRCA2 hereditary cancer with high accuracy. The test also appears to diagnose the biochemical loss of BRCA2 protein in cancers (ie, BRCA2-mutant genotype), which will usually but not always agree with the presence of a germline BRCA2 mutation found by susceptibility testing by DNA sequencing of blood samples.
authors.affiliation: Department of Pathology, University of Colorado Health Sciences Center, Aurora, CO, USA.
authors.forename: Patrice
authors.initials: P
authors.lastname: Watson
authors.forename: Rita
authors.initials: R
authors.lastname: Lieberman
authors.forename: Carrie
authors.initials: C
authors.lastname: Snyder
authors.forename: Vanessa J
authors.initials: VJ
authors.lastname: Clark
authors.forename: Henry T
authors.initials: HT
authors.lastname: Lynch
authors.forename: Jeffrey T
authors.initials: JT
authors.lastname: Holt
mesh_terms: D024682:BRCA2 Protein / Q000032:analysis*; D001706:Biopsy; D001943:Breast Neoplasms / Q000235:genetics* / Q000473:pathology; D045744:Cell Line, Tumor; D005260:Female; D024522:Genes, BRCA2; D006579:Heterozygote; D006801:Humans; D007150:Immunohistochemistry; D009154:Mutation
chemical_list: D024682:BRCA2 Protein