Changing drug treatment for women with early breast cancer can reduce the risk of the disease recurring or spreading by up to 40 percent, Austrian researchers said on Friday.

Tamoxifen, a drug that interferes with the activity of the female hormone oestrogen, has been the standard treatment following surgery for women with hormone sensitive tumors. But scientists at the Vienna Medical University in Austria said varying the therapy with a drug called anastrozole produced better results in older women past the Menopause.

“Switching from tamoxifen to anastrozole after two years is more beneficial for the patients than staying on tamoxifen,” Professor Raimund Jakesz, the lead researcher, said in an interview.

Anastrozole, which is produced under the brand name Arimidex by AstraZeneca Plc, belongs to a class of drugs known as aromatase inhibitors. They work by blocking the production of the oestrogen in women.

Oestrogen is linked to the development of cancer. Most cases of the disease are in postmenopausal women.

The Austrian researchers compared the impact of the two treatments on more than 3,000 women who took part in two trials. After two years on tamoxifen, about half the women were randomly selected to receive anastrozole for three years, while the others continued with the original drug.

Jakesz and his team said that after two years of follow-up, women given anastrozole had up to a 40 percent lower risk of local and distant recurrences and of cancer in the other breast.

The drug does not work in younger women, and it may increase the risk of fractures. More patients in the anastrozole group had broken bones, although there were fewer cases of blood clots.

Breast cancer is one of the most common cancers in women. More than a million cases occur worldwide each year, according to the International Agency for Research on Cancer in Lyon, France.

“Although further investigation is necessary…this analysis confirms that post-menopausal women who receive tamoxifen as adjuvant therapy should be switched to anastrozole after two years of treatment,” Jakesz added.

His results are published in The Lancet medical journal.

In a separate study published in the British Medical Journal, researchers at the University of Sydney in Australia said a woman’s risk of developing breast cancer after taking Hormone replacement therapy (HRT) to relieve the symptoms of Menopause might be lower than previously thought.

They found that HRT increases a woman’s cumulative risk of the disease but only slightly. Use of oestrogen only, and of combined oestrogen and progestogen hormone therapy, at age 50 for about 5 years, hardly had any impact.

However, taking combined therapy for 10 years did raise the cumulative absolute risk by 7.7 percent.

Earlier research had suggested combined therapy could double a woman’s normal risk of developing the disease.

Combined HRT is the preferred type of replacement therapy in Europe because it lessens the risk of cancer of the womb, which is linked with oestrogen-only HRT.