Exelixis Zeroes in on Lead Drug, Sees Activity in the Bones of Prostate Cancer Patients

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have their tumors remain in check (61 percent to 35 percent), to have pain relief (83 percent to 43 percent), and to reduce or eliminate dependence on narcotic painkillers (68 percent to 33 percent), Exelixis said.

Once patients’ tumors progressed, there was an opportunity for them to go into another phase of the study in which they were randomly assigned to get another round of the Exelixis drug or a placebo. At that point, researchers found that patients’ tumors were kept in check for a median time of 21 weeks on the Exelixis drug, compared with about six weeks for the placebo. The overall number of patients in this group (31) is small, but the difference was statistically significant, and the Exelixis drug was shown to offer an 87 percent reduction in risk of a patient’s disease spreading.

There were significant side effects reported with this treatment, which doctors will surely be scrutinizing at ASCO. Fatigue (16 percent), high blood pressure (6 percent), a tenderness/peeling of skin known as hand-foot syndrome (6 percent), decreased appetite (5 percent), nausea (4 percent), and vomiting (4 percent) were the most common moderate to severe side effects reported. One patient on the drug died from unexplained causes at Week 33 in the study, according to an Exelixis statement. About half (51 percent) of patients had to reduce the dose at least one time, Exelixis said.

The safety profile of the drug, Morrissey says, was consistent with prior studies, and consistent with other drugs in its class. There was “nothing overall surprising,” he says.

Still, the unexplained death is bound to raise at least a few questions at the ASCO conference. Earlier in the weekend, Exelixis presented data from 70 patients on the treatment for their ovarian cancer, and found that 73 percent had at least some tumor shrinkage, and 24 percent had what is considered significant shrinkage of their tumors. Researchers don’t yet have data to report on whether the drug keeps tumors from spreading for a meaningful length of time, or whether it helps extend lives.

The side effect profile in these patients appeared similar to what was observed in prostate cancer patients, although two deaths in the ovarian cancer patients were reported by researchers as drug-related. One was characterized as an “enterocutaneous fistula,” which the National Institutes of Health defines as an abnormal opening that allows the content of the stomach or the intestines to leak. The other patient who died had an intestinal perforation, Exelixis said.

Cory Kasimov, an analyst with JP Morgan who reviewed the ovarian cancer data, said yesterday in a note to clients that “overall, cabo clearly looks like an active agent in this setting,” but said it’s hard to put the findings in context without a full report on survival times or the length of time tumors stay in check. He also noted the two deaths, “which has prompted some incoming questions.”

David Miller, president of Biotech Stock Research, said the bone scan data “look great” in prostate cancer patients, especially when it’s shown to be linked to better clinical outcomes, like less pain. But Exelixis did report six deaths out of the total database of 490 patients in the trial. The deaths of the patients “are always a concern,” that need to be inquired about more, Miller said.

Exelixis will have more to say about all of this on a conference call with investors later today from Chicago, at 7 pm Eastern/6 pm Central/4 pm Pacific.

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