Impact of Erector Spinae Plane Block on Chronic Postsurgical Pain in Breast Cancer Patients

Inclusion Criteria: 1. Age of 18 years or over, but less than 85 years; 2. Scheduled to undergo mastectomy for primary unilateral breast cancer. Exclusion Criteria: 1. Previous breast cancer surgery with an incision of \>2 cm; 2. Chronic opioid dependence or long-term intake of analgesic medicines (\>3 months); 3. Any contraindication to erector spinae plane block, including intrathoracic infection, infection at the puncture site, cancer invasion of the puncture site, severe spinal deformity, history of spinal surgery, and severe coagulopathy; 4. Inability to communicate in the preoperative period because of profound dementia, deafness, language barriers, or end-stage disease; 5. History of malignant tumor in other organs, or a current combination of malignant tumor of other organs; 6. History of coronary heart disease (diagnosed coronary stenosis, previous myocardial infarction, previous percutaneous coronary intervention or coronary artery bypass grafting); preoperative hepatic or renal impairment (alanine transaminase and/or aspartate transaminase ≥2 times of upper limit of normal, or serum creatinine\>133 µmol/L); history of peptic ulcer or hemorrhage; ASA classification IV or above; 7. Allergy to ropivacaine.