Olaparib, a new drug, may help thousands of women suffering from genetic breast cancer, if results of the first tests on patients are to be believed.
The researchers behind the study tested the drug on 54 women with advanced genetic breast cancer, and found that the drug olaparib could stop the growth of tumors and shrink them in more than 40 per cent of cases.
In fact, one patient's tumor disappeared completely after treatment with the drug.
A large number of cases of breast cancer are caused by defects on the BRCA-1 and BRCA-2 genes, which put women at much higher risk of developing aggressive cancers of the breast or ovaries.
And, usually, women who test positive for the mutations have their breasts removed as a precaution, because they have an 80 per cent risk of developing breast cancer in their lifetime.
Olaparib, made by AstraZeneca, is the first of a new class of drugs specifically designed to treat BRCA-related cancers to be tested on patients.
Scientists have said that if further tests prove to be successful, they could be used at an early stage to treat or prevent disease occurring within affected families.
Andrew Tutt, director of the Breakthrough Breast Cancer Research Unit at King's College London, who led the trial, said that the results for olaparib were "very promising".
"We are hopeful that olaparib could provide a targeted treatment for women with BRCA-related breast cancer. Some women also develop breast cancer before they know they are carrying the gene, or see it recur if they have been diagnosed previously," Times Online quoted him as saying.
Olaparib works by blocking a protein that makes cancer cells which have a BRCA fault unable to repair their own DNA, which causes the cancer cell to die and means that the tumor should either stop growing or get smaller.
As the drug works in a targeted way, it kills cancer cells while leaving healthy cells alone in a way that chemotherapy does not, which could help to reduce the punishing side-effects of cancer treatment.
In the study carried out at hospitals in Britain, Europe, the US and Australia, 27 patients took 100mg oral doses of olaparib while another 27 took 400mg doses.
The researchers observed that over 40 per cent of tumors in the higher dose group reduced significantly in size, while all tumors were prevented from progressing for an average of six months.
Tutt said that orlaparib might also have potential as an early-stage or preventative treatment.
He added: "It is important to remember this drug is at a very early stage of development."
The findings were presented at the American Society of Clinical Oncology conference in Orlando, Florida, the world's largest gathering of cancer scientists.