This is a pilot study of the pectoral nerves block (PECS) in patients with persistent pain after breast cancer surgery.

This study is in 2 parts: Part 1 is a description of the anatomy of the PECS block in pain free, unoperated patients using ultrasonography (non invasive). Part 2 is the administration of the block to patients that have persistent pain after breast cancer surgery. Before and after the block we will take a detailed pain history and do neurophysiological tests called quantitative sensory testing (QST). These tests assess the patients' ability to feel warmth, cold and test their thresholds for pain. The block is then administered using ultrasound guidance and 20mls of 0.25% bupivacaine is injected in the pectoral muscles on the side with pain. Thirty minutes after the block, the pain is re assessed and the QST is repeated.

Inclusion Criteria:

• Female patients, aged 18 years or over, treated for breast cancer
• Patients with persistent pain in the breast after surgical treatment for breast cancer. Their pain score must be 4 or more on the numerical rating scale (NRS).

Exclusion Criteria:

• breast surgery within the last 12 months
• previous cosmetic surgery
• bilateral breast cancer (receiving bilateral intervention)
• pregnant or breast feeding
• neurological disease
• on-going treatment for severe mental illness or who abuse alcohol or drugs
• are unable to understand written or spoken Danish or English
• lack mental capacity to give informed consent or cooperate with the neurophysiological testing
• an allergy to amide local anaesthetics
• pacemaker in situ
• received treatment outside guidelines and recommendations from the Danish Breast Cancer Co-operative Group (DBCG)