Study confirms long term benefits of tamoxifen are relevant to all women who take it for five years

Taking tamoxifen for an extra five years benefits women with breast cancer that has not spread to the lymph glands (node negative disease), as well as women where lymph node spread was found at operation, updated research from the University of Birmingham being presented at this year's European Cancer conference* demonstrates.

The risk of dying from breast cancer over the next 5 years is halved in women who take tamoxifen for ten years rather than five. Benefits are only seen for women with hormone-sensitive cancers - the most common kind of breast cancer - but are seen in women of all ages.

The Cancer Research UK study showed in June this year that oestrogen receptor positive breast cancer patients taking tamoxifen for longer than the recommended five years are better protected against recurrence and are less likely to die from the disease.

And now, the researchers have shown that this benefit is seen in all women –women with node negative and node positive cancer and in pre- and post-menopausal women. This is of particular significance as aromatase inhibitors, the newer hormonal drugs, only work in post-menopausal women, and so younger breast cancer patients are more reliant on tamoxifen.

The 'aTTom' study** looked at almost 7,000 women with breast cancer who, after five years of taking tamoxifen, either continued taking the drug for another five years or stopped treatment. 

Among women who took tamoxifen for 10 years, 25 per cent fewer had recurrences of breast cancer after 10 years and 23 per cent fewer died, compared to women who took the drug for just five years.  

Dr Daniel Rea, clinical lead researcher at the University of Birmingham presenting the updated results at the ECC meeting in Amsterdam on Sunday, said: "The finding that women with node negative breast cancer derive a clinically useful benefit is important as this is increasingly more common than lymph node positive disease.  

"Tamoxifen is cheap and widely available so these findings are already being implemented thus having an immediate impact on breast cancer treatment.

"Doctors are now likely to recommend continuing tamoxifen for an extra five years and this will result in many fewer breast cancer recurrences and breast cancer deaths worldwide. 

Around 75 per cent of breast cancers are oestrogen receptor positive and may benefit from hormone therapy. The female sex hormone oestrogen encourages breast cancers to grow by activating oestrogen receptors. Tamoxifen blocks these receptors, reducing the chance of breast cancer returning after surgery or developing in the other breast.  

Despite the benefits of tamoxifen in preventing breast cancers from returning, it does have side effects.  Women taking tamoxifen can experience side effects similar to menopausal symptoms, such as night sweats and hot flushes. Rare but serious side effects of tamoxifen include increased risk of endometrial cancer (cancer of the lining of the uterus), blood clots, and stroke.  Doctors and patients will have to make case by case individual assessments of the risks and benefits of continuing tamoxifen. 

In this study no increase in the incidence of stroke was observed with 10 years of tamoxifen therapy, though endometrial cancer risk was higher with longer treatment. 

Endometrial cancer is often detected early, when it is usually curable; the researchers estimate that for every endometrial cancer death that occurs as a side effect of long-term tamoxifen, there would be 30 deaths from breast cancer prevented. Even where the risk of a recurrence has been regarded as low such as node negative cancers longer tamoxifen may still be appropriate as the reduction in risk of cancer recurrence show that taking tamoxifen for longer than 5 years  clinically worthwhile

Professor Richard Gray, based at the University of Oxford who presented the earlier aTTom results at ASCO in June this year, said: "Five years of tamoxifen is already an excellent treatment but there have been concerns that giving it for longer might not produce extra benefits and could even be harmful. The aTTom study establishes that the benefits of taking tamoxifen for longer greatly outweigh the risks for almost all women with hormone-sensitive breast cancer."

Kate Law, director of clinical research at Cancer Research UK, said: "Large clinical trials like aTTom are vitally important to understand how drugs such as tamoxifen work and how best to use them. We need these sorts of studies so we can be sure the benefits from cancer drugs outweigh the side-effects that they may have."