(Reuters) - Staff reviewers at the U.S. Food and Drug Administration said AstraZeneca Plc's experimental ovarian cancer drug olaparib showed an 83 percent reduction in the risk of disease progression but questioned whether the result could be reproduced.
The drug, olaparib, is designed as a maintenance treatment for certain women with relapsed ovarian cancer whose tumors are responding completely or in part to platinum-based chemotherapy.
Olaparib blocks the activity of Poly (ADP-ribose) polymerase (PARP), an enzyme that plays a key role in cell repair. The drug is aimed at women with a BRCA gene mutation. Patients in a clinical trial had a seven-month median improvement in progression-free survival.
The staff report, published on the FDA's website on Monday, comes two days ahead of a meeting of outside experts who will discuss whether olaparib's benefits outweigh its risks and whether further data is needed before approval.
The small sample size of the patients in the trial with a hereditary, or germline, BRCA mutation, and the fact that the company identified them retrospectively, "call into question the reliability of the estimation of treatment effect," the review said.
The reviewers noted the data "certainly suggests that most patients will experience some degree of delay in the progression of their disease but that the benefit may be due in part to a control arm that performed unusually poorly.
"The analysis of overall survival suggests no detriment as a result of therapy but no survival difference was seen between treatment arms," the review said.
Olaparib, which would be sold under the brand name Lynparza if approved, is one of several cancer drugs flagged by AstraZeneca in its defense against a $118 billion take-over approach from Pfizer Inc.
AstraZeneca projected that sales of olaparib could reach $2 billion a year, although some Wall Street estimates peg the potential sales as half that.
Ovarian cancer is the fifth leading cause of cancer death in women with an estimated 22,000 new cases diagnosed and 14,270 deaths from the disease in the United States in 2014.
(Reporting by Toni Clarke in Washington; Editing by Bill Trott)
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