The gist: A drug called cabozantinib doesn’t do any better than a steroid treatment when it comes to relieving bone pain in men with metastatic castration-resistant prostate cancer. That was the conclusion of a recent clinical trial that tested the drug in volunteer patients. The trial enrolled men who were suffering from moderate to severe pain despite optimized narcotic medication, and whose cancer had worsened after treatment with docetaxel as well as abiraterone and/or enzalutamide. Some of the men in the trial were treated with cabozantinib, and some with the steroid treatment mitoxantrone/prednisone.
“Exelixis (EXEL) announced Monday that treatment with cabozantinib failed to alleviate bone pain compared to a steroid control in men with advanced, metastatic prostate cancer. A negative outcome from the so-called COMET-2 prostate cancer study of cabozantinib was widely expected given the previously announced failure of the COMET-1 study in September. Still, Exelixis shares fell another 10% to $1.49 — an all-time low — on heightened concerns that ongoing cabozantinib studies in kidney and liver cancer may also prove disappointing.
“A few years ago, there was much optimism for cabozantinib based on phase II data showing the drug cleared bone lesions and reduced pain in advanced prostate cancer patients. Cancer that metastasizes, or spreads, to bones is a serious complication leading to fractures, increased pain and eventual death. While many cancer drugs can shrink or eliminate tumors in soft tissue, few if any had ever demonstrated an ability to clear up bone metastases.
“All too often, promising results from phase II studies don’t pan out when larger, confirmatory phase III studies are conducted. That’s exactly what happened to Exelixis. In the COMET-2 study, 15% of prostate cancer patients with moderate to severe bone pain despite use of narcotics responded to treatment with cabozantinib compared to 17% of patients treated with steroids. Clearly, this is not the results Exelixis had in mind three years ago when reporting on the phase II bone lesion/bone pain data in the phase II study.”