Age ≤ 18 years

Inability to co-operate and give informed consent

Breast cancer not histologically or cytologically confirmed

History of other malignancy within the last 5 years

Current severe, uncontrolled systemic disease or mental disorder

Absence of clinically significant symptoms

Parallel ongoing psychological treatment

Ongoing regular psychoactive medication if dosage has been changed during the last 3 months

No access to the internet

Inability to use a computer and/or smartphone and the internet

Parallel ongoing participation in other interventional study or clinical trial

Assessment by the investigator to be unable or unwilling to comply with the requirements of the protocol

A Guided Online Intervention to Improve Quality of Life in Breast Cancer Patients - a Randomised Clinical Trial