Brief Summary: Patients scheduled for breast surgery due to cancer. Each patient will be treated with intravenous (i.v.) oxycodone - patient-controlled analgesia (PCA). Patients will be allocated to one of three groups: erector spinae plane (ESP) block, sham block, controlled group.

Detailed Description: Only patients who are qualified for an elective procedure of mitral breast surgery may participate in the study. Each patient will be anesthetized generally. The same drugs will be used in each stage of anesthesia. The induction: propofol, fentanyl, rocuronium. The airway will be secured with a laryngeal mask airway (LMA). When there is a risk of aspiration, the patient will be intubated. Then, rocuronium or suxamethonium will be used. The anesthesia maintenance: sevoflurane, fentanyl. The emergence: oxygen, sugammadex or neostigmine a required. After the induction of general anesthesia, an opaque envelope with the selected group will be opened. In the controlled group, the procedure will be continued in the patient's supine position. Women from the ESP and Sham groups will be placed in the lateral position. The operated side will be above. Then, the ultrasound-guided ESP block with saline or ropivacaine will be performed. At the end of the surgery, an anesthesiologist will administer oxycodone intravenously (0.1 mg/KG). After emergence from anesthesia, the patient will be transferred to the postoperative care unit. Vital signs will be monitored. The patient-controlled analgesia pump with oxycodone will be used.