The Phase 2 study, which involved women with the
most common form of breast cancer, found that those treated with
hormone drug letrozole plus Pfizer's palbociclib lived for an
average of 20.2 months before their cancer progressed, compared with
10.2 months for patients given letrozole alone.
The U.S. Food and Drug Administration has granted "breakthrough"
status for palbociclib. Pfizer is still discussing a regulatory
pathway for the drug and has not decided whether to seek accelerated
approval based on Phase 2 trial results, said Mace Rothenberg, chief
medical officer for Pfizer's oncology unit.
Palbociclib is viewed as one of the company's most important
experimental drugs that some analysts believe could eventually claim
annual sales of more than $5 billion, if approved by regulators.
The trial tested the pill, which targets proteins involved in cell
division, in post-menopausal women with locally advanced or newly
diagnosed breast cancer that had spread to other parts of the body.
The women had cancer that was both estrogen receptor positive — meaning tumors grow in response to estrogen — and HER2-negative,
meaning that the HER2 protein is not causing the cancer. Such
patients make up about 60 percent of advanced breast cancer cases.
The initial data showed overall survival of 37.5 months for the
combination treatment, compared with 33.3 months for patients given
just letrozole, an estrogen blocker sold by Novartis AG under the
brand name Femara.
Researchers said that because only about 30 patients in each arm of
the 165-patient trial had died it was still too early to define the
drug's impact on survival.
"The curves are starting to separate ... It hasn't reached
statistical significance, but patients are still being followed,"
said Dr. Richard Finn, associate professor of medicine at the
University of California, Los Angeles, and a lead author of the
Side effects seen in the trial, including low blood cell counts and
fatigue, were manageable, he said in a telephone interview ahead of
the study's presentation on Sunday in San Diego at a meeting of the
American Association for Cancer Research.
[to top of second column]
Hormonal agents, like Femara, have extended survival
for women with estrogen-positive, HER2 negative breast cancer, but
there have been no big advances in treatment for nearly two decades,
said Dr Judy Garber, a breast cancer specialist at Boston's
Dana-Farber Cancer Institute and AACR representative not involved in
the palbociclib trial.
"This is garden variety breast
cancer," she said. "When it recurs, all we really have are other
hormonal agents ... This is the first new drug to really show
Pfizer is conducting Phase 3 trials in breast cancer patients as
well as earlier-stage trials in other types of cancer.
Companies trying to develop treatments similar to palbociclib
include Novartis and Eli Lilly & Co, which presented Phase 1 data at
the AACR meeting.
The small trial found that Lilly's drug, LY2835219, used on its own,
shrank tumors in 25 percent of women with metastatic
estrogen-positive breast cancer, and stabilized the cancer in 55
percent of the same group of women.
(Reporting by Deena Beasley; editing by Anthony Barker)
[© 2014 Thomson Reuters. All rights
Copyright 2014 Reuters. All rights reserved. This material may not be published,
broadcast, rewritten or redistributed.