The hormone tablets prescribed after surgery — such as Tamoxifen — can cause menopause-like symptoms such as hot flushes and severe joint pain.
Kathleen Bennett of the Trinity College research team said analysis “clearly shows that recurrence rates of breast cancer are lowest among the women who stick to prescribed medications after other interventions such as surgery”.
Dr Bennett said those women who stuck with the medication reduced by 50% the chances of cancer returning and cut the risk of death by 25%.
Ann O’Doherty, lead clinical director at the National Breast Cancer Screening Programme, urged women not to quit their treatment over side-effects.
“Go back to your treating doctor and discuss changing your treatment, rather than stopping it,” said Dr O’Doherty. “There are options out there. We know that sticking with your treatment improves survival chances.”
John McCormack, CEO of the Irish Cancer Society, said they would be very concerned if women stopping taking prescribed medication.
Women who take drugs such as Tamoxifen are typically on a five-year course to prevent cancer recurring and evidence is emerging to show they are best protected if they take the drug for 10 years, Dr O’Doherty said.
Ian Barron, lead author of the Trinity study, said it was not enough to simply prescribe hormonal therapy after surgery given the side-effects of the drugs “can be powerful enough to turn people off taking the medication”.
Instead, Dr Barron advised a structured approach to interventions, including:
* Early identification of women’s side-effects;
* Availability of effective pharmacologic and psychological care;
* Switching to alternative hormonal therapies.
Dr Barron said that these approaches “could make a significant impact on patients adhering to their medication, and thereby improve their chances of living longer”.
More than 600 women were involved in the Health Research Board funded-study which appeared this week in the British Journal of Cancer, along with a similar study UK study.
The UK study found almost 40% of women were not completing courses of Tamoxifen. It also found not sticking to treatment halved the time it took for the cancer to recur and that women lost an average of 13 months of reasonable quality of life. Their chances of dying during the study period increased from 17% to 26%.
The Irish study found when women either stopped taking hormonal treatments completely (known as non-persistence), or took them inconsistently (known as non-compliance), the evidence points to an increased risk of breast cancer coming back.