Around 20% of breast cancer patients do not complete prescribed endocrine therapy, such as tamoxifen, according to researchers.
A study involving over 5,500 women found that younger patients and those who had taken hormone replacement therapy (HRT) were less likely to adhere to their medicine.
“A substantial proportion of patients who start this treatment do not complete it”
The study included women with oestrogen receptor-positive breast cancer who collected at least one prescription of aromatase inhibitors or tamoxifen and had five years of follow up data.
Women were identified and prescription information was obtained from the regional registers covering around 60% of the Swedish population.
The data was linked to Swedish national registers with information about factors that could influence adherence. Adherence was calculated from the drugs dispensed – patients were classified as non-adherent if they received less than 80% of the drugs needed over five years.
During the five years, 20% of the women became non-adherent. The strongest independent predictors of non-adherence were younger age, previous use of HRT, marital status, and socioeconomic status – measured by type of employment – the study authors found.
They also found women less than 50 years of age were 50% more likely to be non-adherent than 50-65 year olds, with 5% of all non-adherent cases attributable to being in the younger age group.
“Non-adherence to oral endocrine therapy is the most important modifiable risk factor”
Lim Siew Eng
Women who had used HRT were 57% more likely to be non-adherent than those who had not, and unmarried women were 33% more likely to be non-adherent than married women, they said at the ESMO Asia 2016 Congress in Singapore.
Regarding employment, unemployed women had 60% higher odds to be non-adherent compared to “blue collar” workers. “White collar” women were slightly less likely to adhere to endocrine treatment compared to “blue collar” patients.
Lead study author Dr Wahyu Wulaningsih, from University College London, said: “Adjuvant endocrine treatment such as tamoxifen prevents recurrence and improves absolute survival by 5-10% in patients with oestrogen receptor positive breast cancer, especially when taken long term.
“A substantial proportion of patients who start this treatment do not complete it,” she noted.
“A proportion of breast cancer patients of reproductive age may be concerned about the potential impact of endocrine treatment on fertility which could explain why they are more likely to stop taking the drugs,” she said. “Women who wish to have children after a breast cancer diagnosis need more information about their treatment options.”
Breast cancer patients fail to complete tamoxifen therapy
She added: “Research is needed to find out if there are any biological differences in women exposed to HRT before undergoing endocrine treatment for breast cancer. It could be that they are more predisposed to side effects from endocrine treatment. Personalised approaches may improve adherence in these patients by, for example, tailoring the dosage.”
Dr Wulaningsih suggested that unmarried patients might have less social and emotional support to continue taking endocrine therapy.
She said: “Patient support groups could be strengthened, or developed, to help patients overcome the barriers to continuing treatment. Improving adherence should lead to better outcomes for these patients.”
Dr Lim Siew Eng, a senior oncology consultant at the National University Cancer Institute in Singapore, added: “Non-adherence to oral endocrine therapy is associated with higher recurrence rates, and is the most important modifiable risk factor that can affect breast cancer outcomes.”