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 Ibrance received an accelerated U.S. approval in February 2015 based
on its ability to delay disease progression in an earlier, smaller
Phase II clinical trial, with the condition that the results be
replicated in a larger study in order to gain full approval.
The oral drug, which has a list price of about $10,300 a month, has
quickly gained acceptance among oncologists as an improvement over
prior treatments. Some 28,000 women in the United States have
received Ibrance therapy since the accelerated approval, Pfizer
said.
A confirmatory trial called Paloma-2 studied the treatment with
letrozole, which reduces estrogen production, in 666 post-menopausal
women.
Patients who received the Ibrance combination on average went 24.8
months before the disease began to worsen. That compared with 14.5
months for women who received letrozole and a placebo, according to
a brief summary of data that will be presented next month at the
American Society of Clinical Oncology meeting in Chicago.
The 10-month difference, deemed by researchers to be highly
statistically significant, likely paves the way for full U.S. Food
and Drug Administration approval of Ibrance, also known as
palbociclib. The data will also be used to apply for Ibrance
approval in other major markets, Pfizer said.
"It was a very reassuring study," said Mace Rothenberg, chief
medical officer for Pfizer Oncology, noting that the result was
virtually identical to the earlier study.
The clinical benefit rate for patients taking Ibrance, defined as
the proportion of women whose tumors disappeared, shrank
significantly or had no evidence of growth for at least 6 months,
was nearly 85 percent versus 70 percent for letrozole alone.
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The overall response rate, a measure of significant tumor shrinkage,
was 42.1 percent for Ibrance versus 34.7 percent for the placebo
group. The overall survival benefit could not yet be assessed as
most of the women in the study were still alive.
No new safety issues were observed in the study, Pfizer said.
Serious neutropenia, a decline in white blood cells, occurred in 56
percent of Ibrance patients, which can lead to other health
problems.
However, that did not translate into increased risk of infection or
complications, Rothenberg said.
(Reporting by Bill Berkrot; Editing by Michele Gershberg and Nick
Zieminski)
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