Scientists have developed a vitamin D pill to treat advanced prostate cancer.
Prostate cancer is a major killer
Exposure to Vitamin D from sunlight is known to improve the prognosis of certain cancers.
US drug company Novacea has produced a pill which delivers a concentrated dose of the vitamin without running the risk of side-effects from an overdose.
Chemistry and Industry magazine reports that if clinical trials of the drug - Asentar (DN-101) - are successful it could be available by 2009.
The drug would be given to patients in the advanced stages of the disease, along with chemotherapy drugs.
Professor Nick James, a cancer expert at the University of Birmingham, said the drug had produced impressive results in preliminary phase two trials.
He said patients taking the drug lived for an average of an extra nine months longer than those taking another chemotherapy drug - taxotere - alone.
Professor James said: "On average, patients in the advanced stage of the disease survive about 18 months, so an extension of nine months would be very significant in my view."
Asentar provides levels of vitamin D 50 to 100 times higher than normal.
Patients would be expected to take one tablet once a week with their weekly regime of taxotere for three weeks out of every four.
However, Professor James said it was far from certain that the phase three trials would repeat the success of the earlier tests.
The phase II trial used a less than optimal taxotere regime so the survival rate may have been artificially inflated.
Professor James said vitamin D was known to play a key role in the regulation of several tissues, including the prostate and breast.
He said laboratory work had shown that cancer cells had lost the ability to respond in the normal way to vitamin D, and carried on dividing in an uncontrolled fashion.
Data shows that rates of prostate cancer are higher in countries further away from the equator, where there is less exposure to sunlight.
Professor James said it was possible that the new drug helped to increase the sensitivity of cancer cells to the effect of other chemotherapy drugs.
Dr Julie Sharp, of the charity Cancer Research UK, said: "We would welcome any improvements in the treatment for men with advanced prostate cancer and this drug has shown potential in early trials.
"But the results of the much larger study are needed to fully establish if this treatment is both effective and safe."
Prostate cancer is the second leading cause of cancer death in men. It kills one man every hour in the UK.