A new drug for breast cancer is better than the treatments that are already widely available and can prevent the disease returning for up to eight years, researchers say.

Anastrozole, marketed as Arimidex, is thought to have set a new bench-mark for treating early stage breast cancer in postmenopausal women whose disease is fuelled by oestrogen.

The latest study confirms that the drug produces better results than tamoxifen, which has been a preferred treatment for more than 20 years.

The study, published in The Lancet Oncology medical journal, suggests that the drug continues to work even after a patient stops taking it, with a greater chance that tumours will not return or spread.

Although tamoxifen is credited with saving the lives of 20,000 women since the 1980s, it is estimated that 23,000 new breast cancer patients a year could benefit from anastrozole and related drugs, known as aromatase inhibitors.

Anastrozole was approved for use on the NHS in August and has been prescribed to patients with breast cancer since November.

Continuing trials are also investigating whether the treatment should be offered as a preventive therapy to women whose genes put them at particular risk of developing the disease.

About four in five of the 41,000 women found to have breast cancer each year have passed the menopause and 70 per cent of these have cancers that are exacerbated by oestrogen.

Anastrozole acts by cutting the level of oestrogen circulating in the blood-stream, reducing the cancer risk in so-called receptor-positive cancers.

The study looked at the safety and effectiveness of anastrozole compared with tamoxifen, which is sold as Nolvadex, Istubal and Valodex.

Researchers followed the progress over five years of postmenopausal women with hormone-sensitive early breast cancer who were randomly assigned to either treatment or a combination of the two.

In a previous study, the chances of surviving for more than 68 months (5½ years) were 15 per cent greater for those on anastrozole than for those taking tamoxifen.

In addition, the amount of time that passed before the breast cancer recurred rose by 25 per cent, and there was less cancer spread.

In the latest update on the trial after 100 months (just over eight years), researchers noted that the benefits of anastrozole were maintained even after the treatment was completed. Furthermore, the differences between the two groups in the time it took for the cancer to recur, if it did, increased.

The study also suggested that there was no significant difference in the threat of heart disease between the treatment groups – an area of previous concern.

Although anastrozole can cause loss of bone density and increase the risk of fractures in women taking the drug, a common osteoporosis drug can help to prevent this side-effect, experts say.

The authors concluded: “The findings of this report extend the previously reported superior efficacy of anastrozole over tamoxifen at 68 months of follow-up to 100 months.

We also show a carry-over benefit for recurrence in the hormone-receptor-positive population which is larger than that shown for tamoxifen.”

Margaret Coulton, 61, a retired office worker from Hesketh Bank, near Preston, had surgery to remove a tumour in September 2003 and has been taking anastrozole for nearly four years as part of a clinical trial after initially taking tamoxifen. Switching to anastrozole banished the symptoms she was getting, such as hot flushes, tiredness and nausea, and allowed her to stop taking drugs for depression, another side-effect of tamoxifen, she said.

Cancer charities welcomed the latest results. Emma Pennery, a nurse consultant at Breast Cancer Care, said: “From our contact with hundreds of people living with breast cancer we know that many will be delighted to see this latest evidence of success.”

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