Inclusion criteria:  Diagnosis of primary breast cancer stage I-III Min. 6 months post breast cancer treatment (i.e., surgery, chemotherapy, and/or radiotherapy). Endocrine treatment, e.g., Letrozole or Tamoxifen, and/or Zoledronic acid and/or Herceptin treatment is allowed during study participation Pain corresponding to a min. pain score of >= 3 on pain intensity or pain interference measured by 11-point Numeric Rating Scales (NRSs) Sufficient ability to communicate in Danish Sufficient ability to participate in an online-delivered intervention  Exclusion Criteria:  Metastatic breast cancer (stage IV) Breast cancer recurrence Bilateral breast cancer Other current cancer disease Other current pain condition (e.g., fibromyalgia) Current severe psychiatric disorder (e.g., psychosis) Inability to communicate in Danish Inability to participate in an online-delivered intervention