Cancer Research UK scientists have found that five in six women with increased risk of breast cancer turn down drugs likely to prevent the disease, according to research published in Annals of Oncology.
Researchers at Queen Mary University of London collected data from 26 international studies totalling more than 21,000 women of all ages who were at increased risk of developing breast cancer. The women in these studies were offered a five-year course of preventive medication to lower their risk of developing breast cancer.
Overall just one in six - 16.3 per cent - of women at higher risk chose to take the medication. Those offered the opportunity to take part in trials were more likely to use preventative medications with 25 per cent choosing it compared with nine per cent of women making the decision outside a clinical trial.
The team also examined a separate group of 18 studies looking at how likely the women were to complete a full course of drugs. The studies looked at any medication that is used for breast cancer prevention including tamoxifen and raloxifene, either as given on a clinical trial - or by a specialist, when referred by their doctor.
Of the studies that tracked women's use of preventative medications over time, most reported more than 80 per cent of women took the drugs for at least one year. But this declined over time.
Drugs to block cancer-causing hormones and surveillance with an annual mammogram may be offered to certain women with a family history of the disease when they have a moderate to high risk of breast cancer.
Study author, Dr Sam Smith, from Queen Mary University of London, said: "Our important research reveals that only a small proportion of eligible women make the decision to have preventative medication.
"It's crucial to find out why so many chose not to take the drugs - or stopped taking them before completing the course."
Mum-of-three Trish Jamieson, 62, lost her sister Noreen to breast cancer at the age of 38 in 1992. Because Trish had two close relatives who developed breast cancer when they were quite young she was considered at higher risk and signed up to the IBIS II trial designed to show whether a drug called anastrozole could prevent breast cancer in women at increased risk.
Trish finished taking the pills in March 2011. The results of the trial could help prevent thousands of women from developing breast cancer in the future.
She said: "I lost my sister to breast cancer and this meant I was also at a higher risk of developing the disease. And when I was offered anastrozole as part of the IBIS II trial I decided to take it, being eligible for the trial.
"It's not for everyone but I weighed up the pros and cons - which can include side effects - and decided it was something that I wanted to do. It's definitely a personal choice but I was glad to have been given this option."
Martin Ledwick, Cancer Research UK's head cancer information nurse, said: "We need to find out more about how women at higher risk of breast cancer make decisions about the different ways they can reduce the risk of developing the disease, to make sure that they have the information they need to make the choice that is right for them."