Women with mutations in the BRCA1 gene have a much higher chance of developing breast cancer but also a higher risk of ovarian cancer. These patients have up to a 65% chance of developing breast cancer by the time they are 70 and a 40% chance of ovarian cancer.
Researchers are now arguing that all women under 50 who are diagnosed with triple-negative (TN) breast cancer should also be offered testing for faults in the BRCA1 gene. This could identify hundreds of extra women every year who may benefit from tailored therapy for BRCA1 breast cancer, such as platinum-based chemotherapy.
Clinical trials also suggested a certain type of radiotherapy could help women with BRCA1 mutations more than others.
Women would also be able to tell their families if they have the BRCA1 gene, meaning close relatives could be tested for the hereditary gene.
The research, published in the British Journal of Cancer, looked at more than 300 women with TN breast cancer.
Almost one in five diagnosed under the age of 50 were found to have the BRCA1 mutation. This fault means breast cancer is more likely to develop at a younger age.
Current guidance from the National Institute for Health and Clinical Excellence (Nice) for England and Wales recommends BRCA1 testing is offered if the likelihood of detecting a mutation is greater than 20%.
Clinicians in Scotland have been advised since 2009 to follow the same general rule.
However, based on their findings, researchers from the Institute of Cancer Research estimate more than one in three women with TN breast cancer caused by BRCA1 mutations would not have been tested using the current criteria.
Lead author Professor Nazneen Rahman said: "Women diagnosed with triple-negative breast cancer under 50 should be offered BRCA1 testing."
Professor Peter Johnson, chief clinician at Cancer Research UK, which funded the study, said: "It's important we identify women and their families who carry BRCA1 mutations.
"They're more likely to develop breast and ovarian cancer, so armed with this knowledge doctors can offer targeted screening and tailored treatments to these women.
"The NHS needs to adapt so tests for BRCA1 can be offered to women who are likely to carry the mutation. This will be cost-effective for the NHS in the long term, leading to a substantial reduction in the number of breast and ovarian cancers by offering preventative treatments for those women and their families who are at greatest risk."