In 230 patients undergoing mastectomy, the investigators will compare opioid-free anesthesia (OFA) versus conventional opioid-based anesthesia in terms of chronic pain. The enrolled patients will be randomly assigned into two groups with 1:1 ratio. Chronic pain will be evaluated at 1 year after mastectomy based on the Breast Cancer Pain Questionnaire (BCPQ). Baseline pain sensitivity test and psychologic evaluation will be done before operation.

Study population

1. All of patients will undergo mastectomy with or without immediate breast reconstruction.
2. 230 patients will be enrolled.

Intervention

1. OFA group will be sedated using dexmedetomidine and lidocaine.
2. Conventional opioid anesthesia group will be sedated using remifentanil.

Pain screening

1. Breast Cancer Pain Questionnaire (BCPQ)
2. Pain-detect, HADS, EQ-5D, PHQ-15 (somatic symptom), PCS (pain catastrophizing), BFI (big five inventory), HAM-A&D, Pressure algometry (Pain sensitivity), Quantitative sensory test (pinprick)

Inclusion Criteria:

• All of patients will undergo mastectomy with or without immediate breast reconstruction.

Exclusion Criteria:

• Previous history of breast surgery
• Allergy to drug
• Other cancer history
• Underlying psychologic disorder
• Patients with chronic pain requiring pain killers
• Baseline SpO2 <95%
• Left ventricular EF <40%
• Bradycardia as HR <50 bpm
• BMI >35kg/m2
• Pregnant woman

Patients will be not aware of which type of anesthesia would be applied during operation.