Women who live in fear of a return of their breast cancer could benefit from a drug which scientists yesterday revealed reduces the likelihood by 69%.

The drug, Femara, also significantly reduced the risk of the cancer spreading and was of benefit to women even five years after they had finished standard drug therapies for early stage breast cancer. It raises the hope that women could be offered new long-term options for treatment to help them keep cancer at bay for up to 10 years.

Patients' groups said it would reduce the anxiety experienced by women who are told their cancers could return at any time despite seemingly successful treatments on standard drugs. Cancer specialists suggested that the class of drug which Femara belongs to could eventually replace tamoxifen, the established long-term drug regime.

Femara was used on 1,655 postmenopausal women with early stage breast cancer - the group of women who overall make up about 60% of diagnoses every year.

The results of the clinical trials, presented at the European Breast Cancer Conference in Nice by the drugs company Novartis, revealed a 69% reduction in the risk of breast cancer returning, a 72% reduction in the risk that the cancer would spread and a 47% reduction in the risk of dying from the disease.

"The results presented today provide the first clinical evidence that women can benefit from Femara even years after the completion of standard treatment," said Andrew Wardley, the study investigator at the Christie hospital, Manchester.

Liz Carroll, head of clinical services at Breast Cancer Care, said: "Women who come to the end of tamoxifen therapy can feel very anxious and live with a constant fear that their cancer could return. Now, there is additional hope as this trial shows that women could have a gap between treatment, and still benefit ... and [it] could save many more lives."

Femara, which costs £83 a month, is the trade name for letrozole, one of a group of drugs called aromatase inhibitors (AI) which reduce levels of oestrogen, to which some breast cancers are sensitive.

Michael Baum, professor emeritus of surgery at University College London, said: "This is really good news. AIs are less toxic than tamoxifen and are a fantastic new advance.

"I think what we're going to see in time is AIs replacing tamoxifen as a long term treatment."

The National Institute of Clinical Excellence is due to decide whether the NHS should fund Femara and other AIs in the autumn. The drug has fewer side effects than tamoxifen, which is associated with increased ovarian and endometrial cancers, but it has been linked to decreases in bone density, which is monitored during treatment.

"There are a lot of women who get to five years and think that's great, I've survived and are keen to get off medication, but other women don't want to give up their safety net," said Nicky Wilkes, product manager at Novartis. "It will be a matter of choice for those women whether they move to other drug treatments."