Is it best to expect the worst? Influence of patients' side-effect expectations on endocrine treatment outcome in a 2-year prospective clinical cohort study.

Background: This study aims to determine the role of patient expectations as potentially modifiable factor of side-effects, quality of life, and adherence to endocrine treatment of breast cancer.
Patients and Methods: A 2-year prospective clinical cohort study was conducted in routine primary care with postoperative patients with hormone-receptor-positive breast cancer, scheduled to start adjuvant endocrine treatment. Structured patient-reported assessments of side-effects, side-effect expectations, quality of life, and adherence took place during the first week post-surgery and after 3 and 24 months of endocrine treatment.
Results: Of 111 enrolled patients, at 3 and 24 months, 107 and 88 patients, respectively, were assessed. After 2 years of endocrine treatment, patients reported high rates of side-effects (arthralgia: 71.3%, weight gain: 53.4%, hot flashes: 46.5%), including symptoms not directly attributable to the medication (breathing problems: 28.1%, dizziness: 25.6%). Pre-treatment expectations significantly predicted patient-reported long-term side-effects and quality of life in multivariate models controlling for relevant medical and psychological variables. Relative risk of side-effects after 2 years of endocrine treatment was higher in patients with high negative expectations at baseline than in those with low negative expectations (RR = 1.833, CI 95%, 1.032-3.256). A significant interaction confirmed this expectation effect to be particularly evident in patients with high side-effects at 3 months. Furthermore, baseline expectations were associated with adherence at 24 months (r = -0.25, P = 0.006).
Conclusions: Expectations are a genuine factor of clinical outcome from endocrine treatment for breast cancer. Negative expectations increase the risk of treatment-specific side-effects, nocebo side-effects, and non-adherence. Yet, controlled studies are needed to analyze potential causal relationships. Optimizing individual expectations might be a promising strategy to improve side-effect burden, quality of life, and adherence during longer-term drug intake.
Trial Registration: ClinicalTrials.gov Identifier: NCT02088710.
(© The Author 2016. Published by Oxford University Press on behalf of the European Society for Medical Oncology. All rights reserved. For permissions, please email: journals.permissions@oup.com.)