Washington, Dec 5 (IANS): A new drug, cabozantinib, produced dramatic and rapid effect on prostate cancer that had spread to the bone, according to an American study.

About two-thirds of patients treated with the drug showed improvements on their bone scans. These bone scans assess the degree to which cancer is in the bone. Improvements on these scans suggest a response to the drug.

"The effects of cabozantinib on bone scans are unprecedented in the treatment of prostate cancer," says David C. Smith, professor of internal medicine and urology at the University of Michigan Medical School, who led the study, the Journal of Clinical Oncology reports.

Cabozantinib is designed to target two important pathways linked to the growth and spread of prostate cancer. The drug had the most effect on tumours that had spread to the bone, which is the major site where prostate cancer spreads, according to a Michigan statement.

These tumours are typically very challenging to treat once they become resistant to hormone-based therapies. In addition to the improvements on bone scans, 67 percent of patients with bone ache reported an improvement in pain control and 56 percent cut down or eliminated painkillers after treatment with cabozantinib.

The trial had enrolled 171 men with castration-resistant prostate cancer, meaning their tumours no longer responded to hormone-based therapies.

Prostate cancer statistics: 241,740 Americans will be diagnosed with prostate cancer this year and 28,170 will die from the disease, according to the American Cancer Society.