Programme: The Genetics of Breast Cancer
Inherited mutations in BRCA1 and BRCA2 are associated with a high risk of breast cancer in some families, and diagnosis of gene defects is now possible at the DNA level. However, current risk estimations have been derived from selected kindreds with many cases of breast cancer and may thus be strongly biased. Evaluation of population-based series of breast cancer patients unselected for family history is necessary to determine more accurately the cumulative and attributable risks of specific BRCA1 and BRCA2 mutations. This study will quantitate the hereditary breast cancer burden in the Netherlands, provide estimates of cumulative and attributable risks, and might reveal unknown genotype-phenotype correlations, all of which are absolute prerequisites for proper genetic counseling. These results will provide the basis for further implementation of genetic screening in the routine clinical practice of breast cancer patient management. Such screening could be important especially for very young breast cancer patients and their family relatives.Plan of investigation Blood samples from a projected 2,000 consecutive breast cancer patients under the age of 75 will be collected during the years 1997-2001, as well as from an age-matched control group of 500 healthy women. Family history of all breast cancer cases will be recorded at the time of accrual, as well as information on known risk factors such as reproductive history. These samples will be investigated for variants in the BRCA1 and BRCA2 gene sequences, after informed consent has been obtained.
In addition to the prospective series (P1 at DDHK, P2 at LUMC), we have also initiated DNA analysis of 2 retrospective series (DDHK: cases with invasive breast cancer diagnosed under 40 during 1985-1995, NR1=363; LUMC: cases with invasive breast cancer diagnosed any age during 1984-1996, NR2=690). The number of cases accrued in the prospective series is now 264 (11/1998 data). While we originally projected only to collect data on family history, we have now also developed questionnaires to collect information on other breast cancer risk factors. As a control for gene and polymorphism frequencies in the general population, we have collected blood lymphocytes from 300 healthy donors, self-referring to the bloodbank Leidsenhage (locale: Leiden/The Hague). The mutation screening modality we are currently developing is designed to analyse large numbers of samples in a relatively cost-effective way, as well as to have the highest sensitivity possible under these restrictions. This development will entail 3 phases: I. proof of principle on BRCA1, including multicolor multiplex PCR, high-throughput testing, and validation of sensitivity; II. Design of combined BRCA1/BRCA2 multiplex PCRs; III. optimization of gel-running conditions to allow the detection of frameshifting as well as base- substituting mutations by CSGE on an ABI377 machine. Phases I and II have been completed and phase III is being carried out now. We have applied the phase I-test, covering ~80% of the currently known Dutch BRCA1 mutation spectrum, to 648 cases of the LUMC-series, and have identified 11 cases as carrying a BRCA1 mutation (Table).