London, Dec 9 (IANS): Five in six women with increased risk of breast cancer turn down drugs that are likely to prevent the disease, finds cancer research scientists in Britain.

"Our important research reveals that only a small proportion of eligible women make the decision to have preventative medication," said study author Sam Smith from the Queen Mary University of London.

"It's crucial to find out why so many chose not to take the drugs -- or stopped taking them before completing the course," Smith added.

Researchers collected data from 21,000 women of all ages at increased risk of developing breast cancer.

The women in these studies were offered a five-year course of preventive medication to lower their risk of developing breast cancer.

Drugs to block cancer-causing hormones and surveillance with an annual mammogram may be offered to certain women with a family history of the disease when they have a moderate to high risk of breast cancer.

The results of the trial could help prevent thousands of women from developing breast cancer in the future.

Those offered the opportunity to take part in trials were more likely to use preventative medications with 25 percent choosing it, compared with nine percent of women making the decision outside a clinical trial.

Overall just one in six of women at higher risk chose to take the medication.

The team also examined a separate group of 18 studies looking at how likely the women were to complete a full course of drugs.

Most of the studies reported more than 80 percent of women took the drugs for at least one year. But this declined over time.

The research was published in Annals of Oncology.