The purpose of this study is to evaluate the role of patients' response expectations for nocebo side effects, quality of life and adherence during adjuvant endocrine treatment (AET). Furthermore, this study analyses the effects of a structured treatment information on patients' satisfaction with information, response expectations, knowledge and adherence.

The majority of breast cancer patients discontinues today's standard adjuvant treatment (endocrine therapy) due to side effects and reduced quality of life. Thereby, most side effects are unspecific, suggesting a role of psychological factors as patients´ expectations (nocebo effects). Moreover, patients are not informed sufficiently about their treatment.

Using a longitudinal design, the nature and onset of adverse side effects and their association to treatment related expectations are investigated. Postoperative patients with hormone receptor-positive breast cancer are assessed before the start of adjuvant treatment. All patients receive standardized, additional information about endocrine therapy. Expectations about side effects, knowledge and satisfaction with the enhanced information are assessed before and after informing patients. Side effects, quality of life and adherence are measured three months, two and five years after start of medication intake.

It will be analyzed if patients' response expectations predict side effects and quality of life during medication intake to provide insights into pathways of clinical nocebo effects. Further, this study examines the effects of a structured treatment information on patients' satisfaction with information, response expectations, knowledge and adherence. The study findings promise significant advances in the clinical nocebo research with strong implications for clinical and research practice.

Inclusion Criteria:

• Post surgery women with estrogen receptor positive breast cancer scheduled to start first-line adjuvant endocrine therapy with Tamoxifen (+/- GnRH) or a third generation Aromatase inhibitor at the Breast Cancer Centre
• Sufficient knowledge of German language and ability to give informed consent
• Age of 18 and more

Exclusion Criteria:

• Presence of a serious comorbid psychiatric condition (schizophrenia or addiction, severe depression or anxiety)
• Presence of a life threatening comorbid medical condition

Primary care clinic