Scientists say they have made a breakthrough in the treatment of breast cancer by using the targeted cancer drug olaparib after chemotherapy.

A major trial in the use of olaparib at an early stage has shown that giving women the drug following chemotherapy significantly reduces the risk of inherited breast cancer returning or spreading.

The trial showed that after a median 2.5 years of follow-up, 85.9% of patients were free of their cancer, compared with 77.1% who had received a placebo. This represented a 42% overall drop in the risk of cancer returning.

Similarly, 87.5% of olaparib patients were alive and free of disease which had spread to other parts of their body, compared with 80.4% who were given a placebo, a 43% drop in the risk of cancer spreading via distant metastases.

Until now, olaparib has been used for advanced cancers. But the study – dubbed the OlympiA trial – has now demonstrated its effectives at the early or “curative” stage, researchers say.

The olaparib trial has been described as a major breakthrough in the battle against breast cancer (Rui Vieira/PA)

The trial was conducted by a series of international partners, including London’s Institute of Cancer Research (ICR), with the results released on Thursday at the American Society of Clinical Oncology (ASCO) annual meeting and published in The New England Journal of Medicine.

The ICR said the trial suggested olaparib, which exploits a genetic weakness in cancer cells, “could become a new treatment option to reduce the risk of recurrence or metastasis in women with inherited forms of high-risk early breast cancer – and could lead to more patients being cured”.

OlympiA steering committee chair Professor Andrew Tutt, professor of oncology at the ICR, said in a statement: “We are thrilled that our global academic and industry partnership in OlympiA has been able to help identify a possible new treatment option for women with early-stage breast cancer who have inherited mutations in their BRCA1 or BRCA2 genes.

“Women with early-stage breast cancer who have inherited BRCA1 or BRCA2 mutations are typically diagnosed at a younger age. Up to now, there has been no treatment that specifically targets the unique biology of these cancers to reduce the rate of recurrence, beyond initial treatment such as surgery, hormone treatment, radiotherapy and chemotherapy.

“This major international study coordinated by the Breast International Group shows that giving olaparib for a year to patients with inherited BRCA mutations after they have completed initial treatment increases the chances that they will remain free of invasive or metastatic breast cancer.”

Prof Tutt said olaparib had the potential to be used “as a follow-on to all the standard initial breast cancer treatments to reduce the rate of life-threatening recurrence and cancer spread for many patients identified through genetic testing to have mutations in these genes”.

He added the frequency of significant side effects from the drug in the study was relatively low.

The ICR’s chief executive, Professor Paul Workman, said: “Olaparib was the first cancer drug in the world to target inherited genetic faults. It is also now the first targeted drug to have been shown to effectively treat patients with inherited mutations and early-stage breast cancer, potentially curing some women of their disease. This is a major breakthrough.

“It’s fantastic that decades of ICR science into identifying cancer’s weaknesses – alongside academic, charity and industry partners in the UK and worldwide – has led to global trials which are now changing the outlook for patients. I am now keen to see this new treatment be approved and made available to patients in the UK and worldwide as fast as possible.