Breast cancer is one of the most common types of cancer among women worldwide. (1) Breast-conserving surgery or mastectomy is indicated for the majority of patients with this type of cancer. (2) Postoperative pain is frequent in this population, with almost 50 % experiencing acute pain and 25-60 % subsequently live with chronic pain. (3-5) Today no golden standard for postoperative pain management regarding breast cancer surgeries exists, and there is definitely room for improvement. Especially considering the large population of women with breast cancer and consequences of acute and chronic pain, such as prolonged recovery and affected quality of life. (6,7) With the present study, we aim to optimise postoperative pain treatment and investigate the effect of a standardised multimodal postoperative analgesic regimen based on previous recommendations. (4,8,9)

All patients scheduled for breast conserving surgery or mastectomy with or without ALND or SLNB at Zealand University Hospital, Roskilde, will be invited to participate in the study. When the patients arrive for preoperative preparation on the day of surgery, one of the investigators will be responsible for a thorough oral information regarding the purpose of the study and all relevant participation requirements. The conversation will take place in a closed room, and the informed consent form will be obtained if the patient decides to participate.

Furthermore, patients will be informed that participation is voluntary and that a wish for withdrawal will be granted immediately.

The informed consent will grant the investigators direct access to data in the patients' electronic files to ensure the information necessary for the study. The patients also consent to complete the questionnaires in the seven-day follow-up period, and that the investigators can reach them by phone.

Completion of the study It is considered a completion of the study when a patient has signed the informed consent, has followed the treatment regimen, and answered the questionnaires in the seven-day follow-up period.

If a patient does not complete the study, an account should be given as to whether and how this subject's data is handled in the study - this also replies to drop-outs.

Reasons for withdrawal

- If a patient wishes to withdraw from the study In accordance with the Declaration of Helsinki, patients have the right to withdraw from the study at any time for any reason. The investigators also have the right to withdraw a patient from the study at any time. The reason for withdrawal must be recorded.

Inclusion Criteria:

• Patients scheduled for day-case unilateral breast conserving surgery or mastectomy +/- ALND or SLNB.
• Age ≥ 18 years of age.
• Patients who received written and oral information, and have signed the informed consent form on participation in the study.
• Patients living in the Region of Zealand.

Exclusion Criteria:

• Not able to speak, read, or understand Danish.
• Inability to cooperate and to consent.

All patients scheduled for breast conserving surgery or mastectomy with or without ALND or SLNB at Zealand University Hospital, Roskilde, will be invited to participate in the study.