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Cancer risk for women who stop taking tamoxifen early

Six fewer deaths per 100 women who took tamoxifen for five years

Adrian O'Dowd

Tuesday, 22 March 2011

Women who decide to stop taking tamoxifen for the full recommended five-year period have a higher risk of their breast cancer returning, according to a study published in the Journal of Clinical Oncology.

A large study funded by Cancer Research UK carried out over 10 years has shown the long-term benefits of taking tamoxifen for five years.

Of the nearly 3,500 patients took part in the study, the cancer came back in around 40% of the women who took tamoxifen for five years, compared to 46% among those who took it for two years.

The study by Cancer Research UK and University College London Cancer Trials Centre compared five and two years of tamoxifen in women with early breast cancer.

Between 1987 and 1997, 3,449 patients aged 50 to 81 years with operable breast cancer who had been taking 20 mg of tamoxifen for two years were randomly assigned to either stop or continue for an additional three years.

The researchers collected data on recurrences, new tumors, deaths, and cardiovascular events.

Results showed that, overall, there were 1,103 recurrences and 755 deaths as a result of breast cancer, as well as 621 cardiovascular events, and 236 deaths as a result of cardiovascular events.

They found that 15 years after starting treatment, for every 100 women who received tamoxifen for 5 years, around six fewer experienced recurrence, compared with those who received tamoxifen for two years.

In addition, the study also found the added benefit of taking tamoxifen for five years was that it reduced the risk of developing or dying from heart disease.

This effect was strongest among women aged 50-59 at diagnosis, with 35% fewer women developing a heart condition and nearly 59% fewer deaths as a result.

They concluded: “Taking tamoxifen for the recommended five years reduces the risk of recurrence or contralateral breast cancer 15 years after starting treatment. Women should therefore be encouraged to complete the full course.”

Senior author Dr Allan Hackshaw said: “Our study provides conclusive evidence that taking tamoxifen for five years offers women the best chance of surviving breast cancer.

“Women diagnosed with early stage breast cancer who are prescribed tamoxifen are recommended to take the drug for five years, but we know that many stop after two or three. Worryingly our results suggest that by doing this, they could increase their risk of cancer coming back.”

Kate Law, director of clinical research at Cancer Research UK, said: “It’s vital that doctors and nurses continue encouraging women to finish their course of tamoxifen and providing the necessary support to ensure any side-effects are effectively managed. We would urge anyone who experiences problems taking their medication to consult their doctor without delay.”

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