Findings by Breast Cancer Campaign funded researcher Dr Colin McCowan (University of Glasgow with colleagues from the University of Dundee) released in the British Journal of Cancer today, showed that at least half of women who were prescribed a five year course of anti-hormone breast cancer treatment, in Tayside, Scotland, either stopped taking, or took markedly less than their prescribed doses from the third year of treatment onwards. Women who followed their treatment regime for up to three years but then took fewer than 80% of their pills in the fourth and fifth years were at a higher risk of their cancer returning, and of dying from breast cancer, than women who took over 80% of the prescription over each of the five years.

Dr McCowan and his team at the University of Dundee studied the anonymised details of 3,361 women in Tayside who were prescribed anti-hormone treatments tamoxifen or aromatase inhibitors for five years after their initial treatment. This is the current standard treatment for women with the most common type of breast cancer, oestrogen receptor positive, which accounts for around 40,000 of the 50,000 diagnosed with the disease each year in the UK. These women started taking tamoxifen (2849 women) or an aromatase inhibitor (512 women) between 1993 and 2008.

Using prescription records, researchers calculated how closely women had followed the “one a day” pill regime and for how long, over the full five year treatment duration and also by year. If women had collected less than 80% of their prescription they were classed as having a “low adherence” to their treatment.

They found that during the first year of treatment women collected, on average, 90% of their tablets. Over the next three years this figure dropped to 82%, 77% and 59% respectively. By year five half of the women were collecting 51% or less of their prescription.

The study also confirmed previous findings that women who collected less than 80% of their prescription over the whole five years were more likely to die earlier, than women who collected more of their prescription.

Dr McCowan, said:

“This study shows us that it’s vitally important that breast cancer patients across the UK follow their prescribed treatment regimes on a daily basis for the full five year period.

“We’re now looking at why women are finding it harder to take medication for extended periods of time and we do know that side effects can be a real issue for women on long term treatments such as tamoxifen. This is why women need the support of their clinicians so that they can discuss any problems they are having rather than stopping taking treatments.”

Baroness Delyth Morgan, Chief Executive of Breast Cancer Campaign said:

“Breast cancer treatments are there to give women the best chance of a long and full life after a diagnosis so these findings are hugely worrying. We need to give women clear, helpful and timely communication as well as the best clinical support we can, to find ways to manage what can often be extremely difficult side effects and make it easier for them to continue to take treatments. Taking tamoxifen for ten years has recently been recommended as one of the ways to prevent more breast cancers returning and reduce the chance of women dying so it’s going to be even more important to help women to take drugs for longer periods of time.

“At Breast Cancer Campaign a key part of the research we’re funding is to bring about new and improved, personalised treatments that have fewer side effects as well as finding ways to identify early which treatments will work best for which patients.”