Dexmedetomidine is widely used as an anaesthetic for general anesthesia during surgery. Previous studies in cells and animals show that dexmedetomidine may promote cancer growth. The purpose of present study is to examine whether utilization of dexmedetomidine in patients undergoing surgery for primary breast cancer increases breast cancer recurrence and metastasis, and to investigate its effects on the patients' immune system.

Women diagnosed with breast cancer undergoing elective surgery under general anesthesia will be randomly allocated to dexmedetomidine group or control group. Patients from both groups will receive midazolam, propofol, fentanyl, remifentanil and CIS atracurium for total intravenous anesthesia. BIS value will be controlled between 40-60 during surgery. Patients of dexmedetomidine group will receive a loading does of 1ug/kg dexmedetomidine since 15 mins before induction, and receive another 1ug/kg of dexmedetomidine at a rate of 0.5ug/kg/h for 2 continuous hours during surgery. Patients of control group will receive same amount of normal saline. Patients will be followed up for 36 months to measure the incidence of cancer recurrence and metastasis. Serum form patients of both groups will be collected at 24 h after surgery. The number of CD3+ , CD4+, CD8+ cells and NK cells in the serum will be compared between the two groups. Serum levels of IFN-γ, IL-12，IL-4 and VEGF will also be measured and compared.

Inclusion Criteria:

• ASA grade I-III
• Age range of 18 to75
• Patients diagnosed primary breast cancer
• Patients will have elective mastectomy

Exclusion Criteria:

• with history of breast operation
• Patients diagnosed with inflammatory breast
• Severe mental or physical illnesses(like liver, renal, brain or lung disease)
• with history of opioid addiction
• Patients diagnosed metastatic breast cancer
• Contradictions or an allergy to Dexmedetomidine