* HRD-negative patients show PFS benefit of 3.1 months
* Growing interest in PARP inhibitor cancer drug class
By Ben Hirschler
COPENHAGEN, Oct 8 (Reuters) - Tesaro's experimental drug niraparib improved outcomes for a broad range of women with recurrent ovarian cancer in a clinical study, boosting prospects for the product, which belongs to a closely watched class of new medicines.
U.S. biotech company Tesaro had already cheered investors in June by saying that the study had met the main goal of prolonging survival without disease worsening, but full results were only reported at the annual European Society for Medical Oncology congress in Copenhagen.
The treatment helped patients live longer without their disease progressing. Even those least likely to be helped by the drug, because of their genetic profile, saw a benefit of just over three months, researchers told the meeting on Saturday.
Niraparib is a so-called PARP inhibitor that blocks enzymes involved in repairing damaged DNA, thereby helping to kill cancer cells.
AstraZeneca's Lynparza became first of the new class to reach the market when it won U.S. approval at the end of 2014, but it was only cleared for patients whose cancer tested positive for defective BRCA genes.
Tesaro aims to prove its drug can work more widely, potentially across the entire population of women needing maintenance therapy for ovarian cancer after chemotherapy.
"This is a breakthrough for patients with ovarian cancer," study leader Mansoor Raza Mirza of Copenhagen University told the meeting. "We have never seen such large benefits in progression-free survival (PFS) in recurrent ovarian cancer."
The latest findings showed that various patient populations all responded, with the biggest median PFS of 15.5 months seen in the BRCA mutation group. However, even those with no BRCA mutation and who tested negative to another test called HRD still saw a modest but significant benefit of 3.1 months.
There is now likely to be debate among doctors and investors as to whether this is enough for Tesaro to win very broad approval for its drug or whether it should be reserved for a narrower group of patients based on genetic tests.
Myriad Genetics provided the diagnostic test that was used to recruit patients into Tesaro's drug trial, results of which were also published online in the New England Journal of Medicine.
Interest in PARP inhibitors has grown apace over the last year as drug developers try to target DNA repair mechanisms inside cells as a way to fight cancer.
Other companies with PARP inhibitors in development include Clovis, AbbVie and Medivation, which was recently bought by Pfizer for $14 billion. (Editing by Alexander Smith)