Breast cancer drug works after women stop taking it

A breast cancer drug could offer post-menopausal women long term protection against the disease, even after they stop taking it.

The drug, anastrozole, has been used to treat breast cancer for over 20 years, but is not offered to all women as doctors are unsure about the evidence surrounding its long-term benefits.

Now, results from a 12-year study show that the drug offers women protection against developing breast cancer when they stop taking it after five years.

The study - led by professor Jack Cuzick from Queen Mary University of London - included 3,864 women, 49% of whom experienced fewer incidences of breast cancer, even up to seven years after they last took the the drug.

The findings are important as physicians now have the long-term evidence required for them to offer anastrozole as an effective preventative medicine to other breast cancer drugs.

Physicians can currently offer women at risk of developing breast cancer another drug called tamoxifen. However, data for tamoxifen show that the drug is only effective at reducing breast cancers for 28% of women who take it.

Dr Ivana Sestak, reader in Medical Statistics at Queen Mary, said: “The findings mean that for every 29 women taking anastrozole for five years, one case of breast cancer will be prevented during a 12 year period. Around 49 women would need to take tamoxifen for five years to prevent one breast cancer case during the same period.”

More so, anastrozole doesn’t cause the same kind of long-term side-effects as seen with tamoxifen, which has been reported to lead to endometrial cancer.

Professor Cuzick said: “This is an exciting finding which makes a strong case for anastrozole being the drug of choice for post-menopausal women at high risk of developing breast cancer. Tamoxifen could be offered to the relatively few women who experience serious side-effects from anastrozole.”

Further follow up on anastrozole is still required however to assess if the drug can reduce breast cancer deaths.

Clinical lead professor Tony Howell from the University of Manchester said: “Importantly, this study shows that there are no significant long term side-effects in the five years after completion of anastrozole, particularly no increase in fractures or heart disease.”

Professor Charles Swanton, Cancer Research UK’s chief clinician, said: “Both tamoxifen and anastrozole can be given to women who are at higher risk of breast cancer. Up until now we only knew that tamoxifen has long lasting benefits, so it’s reassuring that this study looking specifically at anastrozole, which has fewer long term side-effects, gives better protection to women years after they stopped taking the drug.

“Doctors may still decide that tamoxifen is more appropriate for some women, but it’s great that there are options. Anyone with questions about these findings, or about their family history and risk of breast cancer, should speak to their doctor, who can help work out which medication is best for them.”

Breast cancer currently affects around 55,000 women in the UK every year and kills more than 11,000.