The presence of a defective breast cancer gene does not reduce the chances of survival if you develop the disease, the Daily Mail and other media sources reported. Women who have one of the three gene mutations known to be associated with an increased risk of developing breast cancer – mutations in the BRCA1 or BRCA2 genes – are "as likely to survive in the long term as other breast cancer patients".
The Daily Mail reported that previous studies had shown that "tumours among women with BRCA1 or BRCA2 [tend] to be more aggressive". However, this 10-year study carried out in 22 Israeli hospitals, found there to be no difference in 10-year survival rates among women with breast cancer, regardless of whether they carried a mutation in the BRCA1 or BRCA2 genes, or no mutations in these genes.
The underlying research was a study looking back at a specific population of Israeli Jewish women with breast cancer, which assessed whether the women had BRCA1 or BRCA2 mutations, and whether this affected what happened to them over the 10 years following diagnosis.
Where did the story come from?
The study was conducted by Gad Rennert and colleagues at the National Cancer Control Centre and Department of Epidemiology in the Carmel Medical Centre, Israel, and the Women’s College Research Institute, University of Toronto, Canada. It was supported by a grant from the National Cancer Institute and was published in the peer-reviewed journal The New England Journal of Medicine.
What kind of scientific study was this?
This cohort study was designed to investigate whether there was an association between the presence of the breast cancer gene mutation and the chances of survival or death from breast cancer or other causes.
Women diagnosed with breast cancer in 1987 and 1988 were identified using the Israel National Cancer Registry which holds details for 95% of Israeli women with breast cancer. DNA analysis was carried out on preserved samples of tumour tissue, obtained from 1,794 women and two BRCA1 gene mutations and one BRCA2 gene mutation, known to be common in Ashkenazi Jewish women, were investigated.
Women were split into three groups: those with a BRCA1 gene mutation, those with a BRCA2 gene mutation, and those without either. Researchers looked at the women’s medical records (available for 86% of the women) to see how tumour characteristics differed between the groups and whether women survived or died over the 10-year study period.
What were the results of the study?
The study found that overall survival rates after 10 years did not differ significantly between the three groups: 49% of women with BRCA1 mutations survived compared with 48% of women with the BRCA2 mutation, and 51% of women with no identified mutations. There was also no difference between the groups in deaths from breast cancer.
What interpretations did the researchers draw from these results?
The researchers concluded that in Israeli women with breast cancer, having one of three common breast cancer gene mutations does not increase the risk of death from the disease when compared with women with breast cancer who were not carriers of these mutations.
What does the NHS Knowledge Service make of this study?
Cohort studies are used to determine the natural history of a disease. This cohort study, published in a highly-respected medical journal was well-conducted and its findings seem reliable.
The few limitations have been acknowledged by the authors:
- Only the three BRCA gene mutations that are most common in Ashkenazi Jewish women were studied, and therefore we can only draw conclusions about the effects of these mutations on survival. Different gene mutations may have different effects on survival. Although these three gene mutations are common among Ashkenazi Jewish women, they may not be as common among women of different ethnic origins.
- Only a small number of the women from the whole cohort had the BRCA gene mutations (8%), therefore some analyses were performed on only a small number of women, for example, those looking at the association between survival rates and tumour characteristics in women with mutations. Results would be more reliable with a larger sample. However, in practice, it may be difficult to obtain larger groups of women to participate in a similar study.
- Information about some tumour characteristics was missing for some women, therefore any association between gene status and these features cannot be established firmly.
Sir Muir Gray adds…
The occurrence of cancer in younger people can lead to cancer developing a reputation of being "more aggressive" because of the great distress caused by cancer and the impact that a small number of cases can have on the public and professional imagination.
Although this study indicates that BRCA-related tumours have no worse outcome, this does not diminish the significance of the BRCA mutation, which has been shown to increase the likelihood of breast cancer in those who carry it.