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 Xtandi, a pill known chemically as enzalutamide, is
already approved to treat patients whose prostate cancer has spread
and who had previously been treated with chemotherapy.
An approval for use prior to chemo could greatly expand the
available patient population and significantly boost sales, as well
as enable Xtandi to better compete with a rival drug from Johnson &
Johnson called Zytiga.
Sanford Bernstein analyst Geoffrey Porges said annual Xtandi sales
could eventually exceed $3 billion with a pre-chemo approval and
data as good or better than Zytiga.
Medivation and its Xtandi commercial partner, Japanese drugmaker
Astellas Pharma Inc, said they expect to apply for the expanded
approval with the U.S. Food and Drug Administration and European
regulators early this year, based on the data from the Phase III
trial called Prevail.
In the 1,700-patient study of men with metastatic prostate cancer
who have failed hormone deprivation therapy but had few or no
symptoms, Xtandi reduced the risk of death by 29 percent and the
risk of the disease worsening, known as progression free survival,
by 81 percent compared with a placebo.
"An 81 percent reduction in risk of progression is really quite
remarkable in prostate cancer," Dr Tomasz Beer, co-lead investigator
of the Prevail study, said in a telephone interview.
"This is the most exciting thing to have a result like this that's
unambiguously positive and offers patients a new treatment option
that's well-tolerated, extends life and controls the disease," said
Beer, deputy director of the Knight Cancer Institute at Oregon
Health and Science University.
LONG-TERM IMPACT
The preliminary results were released on Tuesday ahead of a
presentation of the data on Thursday at the American Society of
Clinical Oncology Genitourinary (ASCO GU) Cancers Symposium in San
Francisco.
Median time to disease progression — the time it takes for the
disease to worsen in half the patients — was 3.9 months in the
placebo group and had not yet been reached for Xtandi.
The full extent of the survival benefit was expected to be presented
at a later medical meeting. But researchers observed a clear
survival benefit from Xtandi even though 40 percent of Xtandi
patients and 70 percent in the placebo group went on to subsequent
therapies that can help to extend survival.
"It tells us that controlling the disease at this point in its
course can have a long-term impact," Beer explained.
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Men taking once-daily Xtandi on average went 17 months longer
than those in the placebo group before requiring chemotherapy — 28
months versus 10.8 months.
Beer said it was important to have an oral drug with relatively
mild side effects that can slow the cancer for these patients as
they are often reluctant to start toxic chemotherapy if they are not
experiencing symptoms.
"Some intervention is necessary. You want to halt the process when
people are feeling well so that they can continue to feel well and
live a high quality of life," Beer said.
The discontinuation rate due to side effects was about 6 percent in
both groups.
"The safety looked excellent. Serious side effects were really quite
uncommon," Beer said.
Xtandi did raise blood pressure in more than 13 percent of
patients versus about 4 percent on placebo, but that was easily
controlled by common hypertension medicines, Beer said.
Serious heart issues were observed in 2.8 percent of Xtandi patients
compared with 2.1 percent in the placebo group, which Beer said
merited further analysis.
But he found it reassuring that there were no reported seizures
associated with Xtandi during the treatment period, which had been
of some concern in earlier studies. Patients with a history of
seizure were excluded from the Prevail trial.
"Based on the science that we see here I'd expect it, once the FDA
has reviewed it, to become a common treatment option for patients in
this situation that's going to help a lot of people," Beer said.
(Reporting by Bill Berkrot in New York;
editing by Matthew Lewis)
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