A drug that unpicks the genetic defences of tumours has added three months to the lives of patients in a rare breakthrough against an incurable form of breast cancer.
Women who inherit weaknesses in their BRCA genes, including the actress Angelina Jolie, have four or five times the average risk of developing the disease.
These cancers, which affect up to 3,000 women a year in the UK, are often particularly hard to treat because a large fraction are “triple negative”, meaning that they are impervious to many conventional breast cancer medicines. They are also the most common form of hereditary breast cancer and are disproportionately likely to develop in younger women.
Scientists have discovered that they can exploit a vulnerability in the tumour’s faulty DNA repair mechanism with a drug called olaparib, which is already prescribed to women with advanced BRCA-linked ovarian cancer. The findings of a 302-patient clinical trial, presented at the American Society of Clinical Oncology conference in Chicago, show that the therapy also has a strong effect against metastatic breast cancers with the BRCA mutations.
Sixty per cent of the women who took the capsules instead of normal chemotherapy had their tumours shrink, compared with only 29 per cent of those who received the usual treatment.
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Olaparib appeared to keep patients alive for three months longer and delayed progression by seven months, compared with four in the case of chemotherapy. It also had significantly fewer side effects.
The drug, which costs about £10,000 a month, works by shutting down the production of the poly ADP ribose polymerase enzyme, a crucial part of a cancer cell’s kit for fixing its own genes.
Mark Robson, a medical oncologist at the Memorial Sloan Kettering Cancer Center in New York, who led the trial, said: “This study is proof of the principle that breast cancers with defects in a specific DNA damage repair pathway are sensitive to a targeted therapy designed to exploit that defect.”
Olaparib was developed in the Breast Cancer Now Research Centre at the Institute of Cancer Research in London. Andrew Tutt, the centre’s director, said the results were “fantastic”. He added: “It is a perfect example of how understanding a patient’s genetics and the biology of their tumour can be used to target its weaknesses and personalise treatment.
“We are getting much better at curing patients with breast cancer that is diagnosed early — but once the disease has spread around the body, it is much more difficult to treat. We need to see more innovative cancer drugs like olaparib being developed to give these women a better quality of life for longer.”