The majority of breast cancer patients discontinue today's standard adjuvant treatment (endocrine therapy) due to side effects and reduced quality of life. Thereby, most side effects are unspecific, thus, not related to the specific pharmacological action of the drug, but to the individual treatment context and patients´ expectations (nocebo effects). The aim of this study is to evaluate a side effect prevention training (SEPT) that optimizes patients' response expectations before the start of pharmacotherapy to prevent nocebo side effects during longer term drug intake. Using a randomized trial, we will study the time course of response expectations and side effects in breast cancer patients receiving either SEPT, standard medical care or an attention-control intervention ("supportive therapy") before the start of adjuvant endocrine therapy. We will analyze the effects of changing pre-treatment expectations on cancer-treatment related side effects, quality of life and adherence 3 and 6 months after the start of endocrine therapy. Moderator analyses will be used to determine predictors of non-specific medication side effects and patients that are at high risk of experiencing them. Furthermore, we will explore the mediating influence of coping behaviours, thereby providing insights into pathways of clinical nocebo effects. The study findings promise significant advances in the clinical application of nocebo research with strong implications for clinical and research practice.
