By Deena Beasley
(Reuters) - 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 Thomson Pharma.
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.
(Reporting by Deena Beasley; Editing by Michele Gershberg and Prudence Crowther)