(Reuters) - AstraZeneca Plc's experimental
ovarian cancer drug, olaparib, showed an 83 percent reduction in the
risk of disease progression, but a U.S. Food and Drug Administration
staff review has questioned whether the result could be reproduced.
The company's shares fell 1.8 percent to 43.89 pounds on the
London Stock Exchange.
Olaparib, one of several cancer drugs AstraZeneca has flagged as
having strong potential in its defense of a $118 billion take-over
bid by Pfizer Inc, is designed as a maintenance therapy for relapsed
ovarian cancer in which tumors have responded completely or
partially to platinum-based chemotherapy.
"AstraZeneca has put up some pretty lofty expectations," said Damien
Conover, an analyst at Morningstar.
The FDA staff report, published on the agency'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 FDA is not obligated to follow the recommendations of its
advisory panels but typically does so.
Olaparib, which would be sold under the brand name Lynparza if
approved, blocks the activity of Poly (ADP-ribose) polymerase
(PARP), an enzyme that plays a key role in cell repair.
Patients in a clinical trial had a seven-month median improvement in
progression-free survival, a benchmark that measures the amount of
time a patient lives without the disease getting worse.
The drug is aimed at women with certain hereditary BRCA gene
mutations that account for an estimated 10-15 percent of all cases
of ovarian cancer, or about 2,000 cases a year in the United States.
Patients with the mutations tend to respond better to chemotherapy
so they are likely to undergo multiple rounds. Periods away from
chemotherapy allow the patient to recover from side effects before
undergoing a new round.
In theory, olaparib would extend that period of recovery time.
The way the company conducted its data analysis, however, has
created some uncertainty about the validity of the results, the FDA
review said. AstraZeneca collected some of the data retrospectively
using archived blood samples, calling into question "the reliability
of the estimation of treatment effect," the review said.
Data suggests most patients will experience some degree of
progression-free survival but the benefit may be due in part to a
control arm that performed unusually poorly, the review said, adding
there was no difference on overall survival between the two
treatment arms.
AstraZeneca has said sales of olaparib could reach $2 billion a
year, although some Wall Street estimates peg the potential sales at
half that figure.
Ovarian cancer is the fifth leading cause of cancer death in women,
with an estimated 22,000 new cases diagnosed and 14,270 deaths in
the United States in 2014.
Olaparib's most common side effects were nausea, fatigue, abdominal
pain, vomiting, diarrhea and anemia.
(Reporting by Toni Clarke in Washington; Editing by Bill Trott and
Paul Simao)
