By Bill Berkrot
(Reuters) - Medivation Inc's drug for advanced prostate cancer significantly delayed progression of the disease and extended survival in a large, late stage study of patients who had not yet received chemotherapy, likely paving the way for an expanded approval of the medicine.
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.
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.
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)