Breast cancer is the most common malignant disease in women. The most affected are women over 50 years of age, but it can also occur in younger people. Risk factors can be: obesity, genetic predisposition, not breastfeeding, smoking, alcohol consumption, diet, early first menstruation and late menopause. Symptoms that point to breast cancer are a lump on the breast, discharge, a change in the shape of the breast, indentation or bulging of the nipple. The diagnosis is made on the basis of clinical examination and history, as well as mastectomy, ultrasound and magnetic resonance imaging. Breast cancer is most often found in the right upper quadrant of the breast. The treatment is multidisciplinary and consists of: chemotherapy, hormonal therapy, immunotherapy, radiation and surgical treatment. Mastectomy is the removal of a breast tumor and the breast itself with or without axillary lymph nodes. It can be for the purpose of treatment or for preventive purposes. In order for the surgical outcome to be as effective and better as possible, quality preoperative and postoperative health care is necessary. It is important to involve the patient in the care itself. The nurse answers the patient's questions and provides the information she wants to know. It is necessary to teach the patient about hand exercises and deep breathing in order to prevent possible complications. After surgery, it is important to support the patient. After surgery, quality of life is an indicator of the effectiveness of disease treatment. The quality of life is defined by subjective impressions of satisfaction and evaluation.