The genetics of breast and ovarian cancer

BRCA1 sequence variations in 160 individuals referred to a breast/ovarian family cancer clinic. Institut Curie Breast Cancer Group

An account of familial aggregation in breast/ovarian cancer has become possible with the identification of BRCA1 germ-line mutations. We evaluated, for 249 individuals registered with the Institut Curie in Paris, the prior probability that an individual carried a mutation that predisposes to these diseases. We chose 160 women for BRCA1 analysis: 103 with a family history of breast cancer and 57 with a family history of breast-ovarian cancer. To detect small mutations, we generated and analyzed 35 overlapping genomic PCR products that cover the coding portion of the gene, by using denaturing gradient gel electrophoresis. Thirty-eight truncating mutations (32 frameshifts, 4 nonsense mutations, and 2 splice variants) were observed in 15% of women with a family history of breast cancer only and in 40% of those with a history of breast-ovarian cancer. Twelve of 25 distinct truncating mutations identified were novel and unique. Most BRCA1 mutations that had been reported more than five times in the Breast Cancer Information Core were present in our series. One mutation (5149del4) observed in two apparently unrelated families most likely originates from a common ancestor. The position of truncating mutations did not significantly affect the ratio of the risk of breast cancer to that of ovarian cancer. In addition, 15 DNA variants (14 missense mutations and 1 neutral mutation) were identified, 9 of which were novel. Indirect evidence suggests that seven of these mutations are deleterious.

Genetic factors in the pathogenesis of breast cancer: their role and relative importance

Aggregation of breast cancer in families is an established risk factor associated with increased incidence of the disease, which is a leading cause of morbidity and mortality among women in this country. Three genes have now been identified that confer increased susceptibility in families with a clear hereditary (i.e., Mendelian) pattern of expression: BRCA1, BRCA2 and p53. However, a significant number of women have an identified family history of breast cancer without clear Mendelian patterns of disease. Such patterns are consistent with the effect of more common genes with lower associated risk. Some evidence is available to implicate three additional genes that fit this category: AT, ESR and HRAS1. An area of active interest is genetically mediated variation in the metabolism of estrogens, a process controlled by several genes, each with more modest effects. The interaction of genes and environmental factors in breast cancer pathogenesis is of considerable public health importance.

A high proportion of novel mutations in BRCA1 with strong founder effects among Dutch and Belgian hereditary breast and ovarian cancer families

We have identified 79 mutations in BRCA1 in a set of 643 Dutch and 23 Belgian hereditary breast and ovarian cancer families collected either for research or for clinical diagnostic purposes. Twenty-eight distinct mutations have been observed, 18 of them not previously reported and 12 of them occurring more than once. Most conspicuously, a 2804delAA mutation has been found 19 times and has never been reported outside the Netherlands. A common haplotype spanning > or = 375 kb could be identified for each of the nine examined recurrent mutations, indicating the presence of multiple BRCA1 founder mutations in the Dutch population. The 2804delAA mutation has been estimated to have originated approximately 32 generations ago. No specific breast or ovarian cancer phenotype could be assigned to any of the common mutations, and the ovarian cancer incidence among 18 families with the 2804delAA mutation was heterogeneous.

Genetics of breast cancer

Familial breast cancer is characterized by young age at diagnosis, an increased risk of bilateral breast cancer, an increasing risk in conjunction with increasing numbers of affected family members, and a strong association with ovarian cancer. At least eight candidate breast cancer susceptibility genes have been identified. Mutations in BRCA1, BRCA2, p53, and the Cowden disease gene are relatively uncommon, are highly penetrant, and produce striking familial clusters of breast cancer. BRCA1 and BRCA2 are the most important of these, accounting for an estimated 80% of hereditary breast cancer and 5 to 6% of all breast cancers. Specific BRCA1 and BRCA2 mutations are of particular importance in population subgroups, such as those identified among Jewish women of central European (Ashkenazi) origin. Mutations in the ataxia-telangiectasia gene and the rare HRAS1 variable number of tandem repeats polymorphisms are much more common but also much less penetrant. They do not produce dramatic familial aggregations of breast cancer but may prove to be responsible for a substantial proportion of all breast cancers if their epidemiologic association with breast cancer is confirmed. Predictive genetic testing for breast cancer risk is under way. Oncologists and primary-care physicians must become familiar with these genetic disorders and the issues surrounding predictive testing in order to make appropriate management decisions about women thought to have a high genetic risk of breast cancer.

The genetics of ovarian cancer: an assessment of current screening protocols and recommendations for counseling families at risk

Although the need for effective ovarian cancer screening is apparent, a highly sensitive and specific screening methodology has yet to be elucidated. 42-44 Given that there are more than 43 million women in the United States older than 45 years of age and that the average cost of a pelvic sonogram is $ 275 (and $ 45 for CA125 screening), the screening of this population is estimated to increase health care costs by $ 14 billion per year. 45 The additional cost of BRCA1 screening varies according to the level of diagnostic effort required to establish BRCA1 gene mutations in a particular family and ranges from $ 295 to $ 1,200 per sample. Assuming an average cost of $ 600 per sample, initial screening of these same women would likely increased costs in excess of $ 25 billion. Current knowledge and technology in ovarian cancer screening has not yet proved beneficial for the general population or for women with fewer than two affected family members. For women with two or more affected family members, there is a 3% chance of that patient being a proband in a hereditary cancer syndrome family. 11,46 In this group, who may be at increased risk for developing a malignancy, heightened surveillance is warranted, although there are still no data to confirm that screening even these high-risk women will reduce mortality. Nevertheless, annual bimanual examination, serum CA125, and transvaginal sonography are recommended among this particular subgroup of women at risk, and are likely to be recommended for young, asymptomatic, at-risk women who screen positive for the 185delAG BRCA1 deletion commonly found in persons of Ashkenazi Jewish ancestry. It is only through prospective, randomized trials that reliable data regarding the risk/benefit ratio of ovarian cancer screening among various populations at risk will be determined. The results of the prospective/randomized PLCO trial and the mature data from ongoing prospective, nonrandomized screening trials for women with a family history of cancer may provide this information and are eagerly awaited.

Breast cancer genetics: family history, heterogeneity, molecular genetic diagnosis, and genetic counselling

Between 5% and 10% of breast cancer cases can be traced to primary genetic factors. Before the discovery of the BRCA1 and BRCA2 genes, if a first-degree relative in direct genetic lineage had hereditary breast cancer or hereditary breast-ovarian cancer syndrome, the best estimate of family members' genetic risk for breast cancer was 50%. Now the lifetime cancer destiny of a patient who carries a BRCA1 or BRCA2 germ line mutation can be determined with an extraordinary degree of precision. However, a major concern facing clinicians is how to use this powerful genetic knowledge without harming the patient. This presentation focuses on the need for (a) compilation of a detailed family history of cancer of all anatomic sites; (b) understanding of the natural history of hereditary breast cancer and its heterogeneous forms and the pathobiology of hereditary breast cancer; and (c) preparation for performance of genetic counseling that is based on the results of DNA sequencing to detect genes related to cancer susceptibility. The discussion addresses the advantages of this molecular genetic movement, which include the abilities (a) to predict who is and who is not at inordinately high risk for cancer; (b) to provide opportunities for highly targeted disease surveillance and management; (c) to give patients the information they need to make appropriate long-term decisions about matters such as procreation; and (d) to give genetic counselors the information they need to appreciate the emotions patients may encounter, such as fear, anxiety, and apprehension, and the ordeal of being subjected to discrimination by insurance companies and employers.

Role of BRCA1 mutation screening in the management of familial ovarian cancer

Families with multiple cases of ovarian cancer have long been observed, and in the past prophylactic oophorectomy has been advocated for women with a history of ovarian cancer in two first-degree relatives. It is now thought that > 90% of familial ovarian cancer is due to inherited mutations in the BRCA1 breast-ovarian cancer susceptibility gene on chromosome 17q. BRCA1 testing is being performed in several academic medical centers on a research basis and is also now commercially available. With the ability to identify inherited mutations in BRCA1, prophylactic oophorectomy and other interventions intended to decrease cancer mortality can be offered specifically to women who carry a mutation, but the optimal strategy for decreasing cancer mortality in BRCA1 families has not yet been determined. To facilitate further clinical and basic research in this field, our group and others have established multidisciplinary hereditary breast-ovarian cancer clinics that offer a wide range of services including BRCA1 testing, genetic counseling, and cancer prevention and treatment.