About one in four breast cancer patients discontinue their prescribed endocrine therapy (ET), according to a study presented at the European Society for Medical Oncology (ESMO) Asia 2016 Congress in Singapore. Furthermore, younger patients and those with prediagnostic use of hormone replacement therapy (HRT) are less likely to adhere to their medication.

“Adjuvant endocrine treatment such as tamoxifen prevents recurrence and improves absolute survival by 5 to 10 percent in patients with oestrogen receptor (ER)-positive breast cancer, especially when taken long term (5 to 10 years),” lead author Dr Wahyu Wulaningsih, research associate, MRC Unit for Lifelong Health and Ageing at University College London, UK, and cofounder of the Philippine and Indonesian Scholars (PILAR) Research and Education, said in a press statement.

“A substantial proportion of patients who start this treatment do not complete it,” continued Wulaningsih. “There is evidence that failure to take the medicine could lead to worse survival. We therefore investigated the reasons for non-adherence so that targeted strategies could be developed.”

Researchers analysed a total of 4,413 women who had at least one dispensation of tamoxifen or aromatase inhibitors (AIs) and 5 years of follow-up. Women were identified from the regional registers of Uppsala-Orebro, Stockholm-Gotland, and Northern Sweden. Patients were classified as nonadherent by using a medical possession ratio (MPR) of <80 percent over 5 years.

Of the patients, 1,131 (25.6 percent) women became nonadherents during follow-up. The predictors of nonadherence were age, marital status, region of diagnosis, private hospital, tumour size, lymph node metastasis, tumour grade, HER2 status, type of surgery, adjuvant chemotherapy, type of ET, prediagnostic HRT, use of symptom-relieving drugs at baseline and during follow-up, baseline score and any increase in Charlson comorbidity index (CCI). [Wulaningsih W, et al, ESMO Asia 2016]

In multivariable analysis, the determinants of nonadherence were younger age (odds ratio [OR], 0.67; 95 percent CI, 0.50 to 0.90 and 0.66; 0.48 to 0.92 for age 50 to 65 and >65 years, respectively), marital status (OR, 1.40; 1.23 to 1.60 for single/divorced/widowed women), socioeconomic status (OR, 1.17; 1.00 to 1.37 and 1.60; 1.16 to 2.21 for white collar and unemployed workers, respectively) and prediagnostic use of HRT (OR, 1.57; 1.28 to 1.93).

“Research is needed to find out if there are any biological differences in women exposed to HRT before undergoing endocrine treatment for breast cancer,” Wulaningsih said. “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.”

She also surmised that single/divorced/widowed patients might have less social and emotional support to complete their prescribed therapy.

These findings somewhat contradict a 2012 population-based study which found during a 3-year follow-up that adherence was positively associated with younger age, large tumour size and being born in the Nordic countries. The previous study also correlated adherence with being married, but no clear association was observed with education or income. [Breast Cancer Res Treat?2012;133:367-73]

“Our study identified subgroups of patients who can be targeted with information on the benefits and consequences of endocrine treatment when it is first prescribed and at subsequent visits,” Wulaningsih 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.”