Scottish women treated for breast cancer are putting themselves at risk of the disease returning by not taking their medication properly, research has shown.
Researchers in Glasgow and Dundee found women prescribed drugs to take for five years after their cancer treatment often stopped taking them before the end of the course.
Campaigners said women had to use their medication correctly to give them the best chance of avoiding the disease recurring.
Dr Colin McCowan, from Glasgow University, and colleagues in Dundee collected information on 3,361 patients with breast cancer treated in the Tayside region. The women were prescribed the anti-hormone treatments tamoxifen or aromatase inhibitors for five years after their initial treatment – the standard therapy for women with the most common type of breast cancer, known as oestrogen receptor positive.
This form of the disease accounts for around 40,000 of the 50,000 cases in the UK each year.
The study included 2,849 women taking tamoxifen and 512 taking an aromatase inhibitor at some point in 1993–2008.
The researchers, writing in the British Journal of Cancer, used prescription records to calculate how closely the women followed their “one-a-day” tablet regime and for how long during the five years they were supposed to be taking the drugs.
During the first year of treatment, women collected on average 90 per cent of their tablets. But over the next three years, this dropped to 82 per cent, then 77 per cent, then 59 per cent. By the fifth year, half of the women were collecting 51 per cent or less of their prescription.
The study found women who followed their treatment regime for the first three years but then took less than 80 per cent of their pills in the final two years were at a higher risk of the cancer returning. It also confirmed previous findings that women who collected less than 80 per cent of their prescription over the five years of treatment were more likely to die earlier than women who collected more of their drugs.
Dr McCowan said: “This study shows us 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, which funded the research, said the findings were “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,” she said.
Her charity is funding research to find better treatments with fewer side-effects, which may encourage women to take them for longer.