One in Five Breast Cancer Patients Nonadherent to Endocrine Therapy

About 20% of women with breast cancer did not complete their prescribed endocrine therapy, according to the results of a study (abstract 62O_PR) presented at the European Society for Medical Oncology (ESMO) Asia 2016 Congress, held December 16–19 in Singapore.

Wahyu Wulaningsih, PhD, a research associate at the Medical Research Council (MRC) Unit for Lifelong Health and Ageing at University College London, and colleagues identified several factors associated with nonadherence, including younger age and prior use of hormone replacement therapy.

“Adjuvant endocrine treatment such as tamoxifen prevents recurrence and improves absolute survival by 5%–10% in patients with estrogen receptor–positive breast cancer, especially when taken long-term (5–10 years),” said Wulaningsih, who is also co-founder of Philippine and Indonesian Scholars (PILAR) Research and Education, in a press release. “A substantial proportion of patients who start this treatment do not complete it. There is evidence that failure to take the medicine could lead to worse survival.”

Using Swedish national registers, the researchers identified 5,544 women diagnosed with stage I to III estrogen receptor–positive breast cancer between 2006 and 2009 in three areas of Sweden. Included women had at least one dispensation of tamoxifen or aromatase inhibitors and 5 years of available follow-up. Women were classified as being nonadherent if they received less than 80% of the drugs needed during 5 years.

The registry data showed that about 20% of women became nonadherent during the 5-year study period. A multivariable analysis showed that the strongest independent factors for nonadherence were younger age, previous use of hormone replacement therapy, marital status, and socioeconomic status.

Specifically, Wulaningsih and colleagues found that women age 50 or younger were 50% more likely to be nonadherent compared with women age 50 to 65 years, with 5% of all nonadherent women falling into this younger age group. Women with a history of hormone replacement therapy were 57% more likely to be nonadherent than those who had no history, and unmarried women were 33% more likely to be nonadherent than their married counterparts.

“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,” Wulaningsih said. “Women who wish to have children after a breast cancer diagnosis need more information about their treatment options.”

Commenting on the findings, Lim Siew Eng, a senior consultant and clinical director of the department of hematology-oncology at the National University Cancer Institute, Singapore, said: “Nonadherence to oral endocrine therapy is associated with higher recurrence rates, and is the most important modifiable risk factor that can affect breast cancer outcomes.”

She noted that it was mainly socioeconomic factors that were identified as risks for nonadherence, not disease or treatment factors. “These risk factors could pinpoint certain groups in which stricter compliance monitoring and better management of side effects might improve adherence rates,” she said.