By Deena Beasley
May 15 An experimental drug from Gilead Sciences
Inc shrank tumors in half of leukemia patients whose
cancer had returned, according to an early-stage trial that
represents a new foray into oncology by the world's biggest
seller of HIV medications.
The pill, idelalisib, is part of a new class of medications
designed to selectively block a type of protein known to promote
tumor growth in patients with chronic lymphocytic leukemia (CLL)
and other types of blood cancer.
The "pretty incredible" results illustrate how a growing
understanding of tumor biology is helping researchers develop
promising new targeted drugs, said Dr Sandra Swain, president of
the American Society of Clinical Oncology, which will feature
the research at its conference in Chicago later this month.
Swain was not involved in the trial.
Researchers said idelalisib, also known as GS-1101, produced
rapid and long-lasting tumor shrinkage in half of the 54 trial
patients treated with the drug alone, stalling disease
progression for an average of 17 months. Patients in the trial
had previously received a median of five other treatments.
CLL, which is typically diagnosed through a routine blood
test, is a slow-growing cancer, and many patients do not require
treatment until they start having symptoms. The vast majority of
patients experience a relapse at some point after initial
treatment with chemotherapy or immunotherapy. And about 20
percent of patients have so-called refractory disease, meaning
that they either relapse within six months or do not respond to
initial treatment at all.
"Drugs like idelalisib are probably going to change the
landscape of the disease in the next few years," said lead study
author Dr Jennifer Brown, assistant professor of medicine at
Dana-Farber Cancer Institute.
Idelalisib works by blocking PI3 kinase delta, a subtype of
PI3K proteins known to promote tumor growth.
Researchers said many trial patients experienced fewer
disease symptoms, while side effects from the drug, including
fatigue, diarrhea and rash, were mostly manageable. Seven
percent of patients left the trial due to side effects.
Gilead, which has dominated the market for HIV drugs and is
vying for a lead position in therapies for hepatitis C, is
testing idelalisib as a treatment for a number of different
blood cancers. The drug is currently in late-stage testing as a
treatment for both CLL and indolent, or slow-growing,
non-Hodgkin's lymphoma (NHL).
Wall Street analysts, on average, have forecast sales of
nearly $500 million a year by 2017 for the drug, according to
Gilead said earlier this month that it would consider filing
for regulatory approval of idelalisib based on pending results
from a midstage trial involving patients with indolent NHL who
had stopped responding to existing therapies. Data from that
trial will be presented at an upcoming lymphoma conference in
Lugano, Switzerland, in late June.