Anastrozole, a popular preventive drug available around the world, has been shown to reduce the risk of breast cancer among women by more than half, according to the results of a new study, holding out promise for millions of women around the world at high risk of suffering from the deadly disease.

According to the findings of an IBIS II trial, funded by the Cancer Research UK charity, taking anastrozole for five years cut the risk of breast cancer by 53 percent among a particular high-risk group, which included post-menopausal women, with fewer side effects as compared to other treatments such as Tamoxifen and Raloxifen.

“This is a significant step for postmenopausal women, who have been identified as high risk,” Tony Howell, scientific director of the charity Genesis Breast Cancer prevention and co-lead author of the study said, adding that the “remarkable” finding provides “another preventative treatment option, which has the potential to save and prolong the lives of thousands of women,” the Telegraph reported.

Results from a separate trial, announced earlier this year, had shown that taking Tamoxifen could reduce the risk of breast cancer by a third, but it leads to side effects such as an increased risk of blood clots and endometrial cancer.

“Women who took anastrozole were only slightly more likely to develop side effects like moderate joint pain than women who took a placebo ‘sugar pill’,” Cancer Research UK said, in a statement. The study also found that taking anastrozole reduced the risk for other types of cancers by up to 42 percent.

“There were 70 cases of other cancers in the placebo group and only 40 in the women taking anastrozole. In particular skin cancer and bowel cancer were significantly less common,” the statement said, adding that this aspect of the result was unexpected and would need further investigation.

Anastrozole, a U.S. FDA-approved generic drug is also cheaper compared to other drug options and costs $3.3 a month in the UK and an average of $16 for a month's course in the U.S.

The trials involved nearly 4,000 post-menopausal women who are at high risk of breast cancer. Half of the women were given 1 mg of anastrozole every day for five years while the other group was given a placebo tablet.

Women in high-risk groups included those who have a family history of breast cancer, such as two or more immediate blood relatives who developed breast tumors, or a mother or sister diagnosed with breast cancer before the age of 50.

According to the study, 40 women in the anastrozole group developed breast cancer after the five-year trial period, while 85 women in the placebo group got the disease.

Many breast cancers are triggered by the hormone, estrogen, and a drug such as anastrozole reduces the levels of the hormone in the body by blocking the aromatase enzyme from producing estrogen, while Tamoxifen stops the estrogen from attaching to breast cancer cells. In menopausal women, estrogen is produced not by the ovaries but by aromatase enzymes found in the breasts and muscles.

According to health workers, the drug could benefit millions of women worldwide and give them a less drastic alternative to mastectomy to prevent the occurrence or recurrence of the disease.

Several celebrities who belong to a high-risk group, such as Angelina Jolie and Kathy Bates, and Sharon Osbourne, the former America's Got Talent judge, have opted for a double mastectomy to remain cancer-free.

Anastrozole was originally developed by British company Zeneca Pharmaceuticals, now AstraZeneca (NYSE:AZN), and is sold under the brand name, Arimidex. However, generic versions of the drug are approved in several countries including the U.S. and India.