A drug that exploits genetic weaknesses in cancer cells can delay some advanced ovarian cancers from getting worse, according to unpublished clinical trial results.

Findings from the phase 3 ARIEL3 trial showed that rucaparib (Rubraca) – a type of PARP inhibitor – boosted the length of time before patients’ disease returned by many months.

Professor Jonathan Ledermann, who led the study at the Cancer Research UK and UCL Cancer Trials Centre, described the findings as a “very important step forward for women with advanced ovarian cancer”.

The findings were presented at the 2017 ESMO Congress in Madrid.

“These results show that rucaparib has the potential to provide an enduring and important clinical benefit in women with advanced ovarian cancer, irrespective of their tumour genetics,” added Ledermann.

PARP inhibitors – a group of drugs that Cancer Research UK scientists helped develop – exploit faulty genes that prevent cells from being able to fix their DNA, for example faults in the BRCA genes. These genetic faults can be passed on through families and raise the risk of developing certain cancers, including breast and ovarian.

The PARP inhibitor olaparib (Lynparza) is already used in the UK to treat some ovarian cancer patients with faulty BRCA genes. Rucaparib has not yet been given the green light for routine NHS use, although in 2015 it was designated a ‘Breakthrough Therapy’ by the US Food and Drug Administration for the same group of women and later approved in 2016.

Among the 550 patients enrolled into the ARIEL3 study, some had inherited BRCA faults while the tumours of other patients carried a genetic indicator showing they had faulty DNA repair machinery, called a biomarker. All women had advanced ovarian cancer and had previously been treated with platinum-based chemotherapy drugs.

Rucaparib was found to increase the length of time before patients’ disease got worse, compared to placebo. And the biggest improvements were found in women with BRCA faults.

In these women the time period before their disease worsened was extended by 77%, from 5.4 months to 16.6 months.

Professor Ruth Plummer, a Cancer Research UK-funded scientist at the University of Newcastle who helped develop rucaparib, said: “This is very exciting data, and a great culmination of the many years of research funded by Cancer Research UK.

“The trial data shows that both patients with inherited ovarian cancer and also the wider group with the tumour biomarker benefit from rucaparib for many months.”