Breast or mammary gland is hormone sensitive organ, therefore prone to pathological changes. Breast disease are in practice generalized to inflammation, benign and malignant tumors. Breast cancer is the most common type of cancer in Croatia and leading cause of death in women. It occurs when normal glandular breast cells change their properties and begin to uncontrollably grow, multiply and destroy surrounding healthy tissue. The risk factors for breast cancer are: family heritage (genetics), prolonged menstrual activity, barren, breast cancer in the earlier background, breast trauma, age, oral contraceptives, hormone replacement therapy and certain other lifestyle habits. Breast cancer is most often manifested as painless node in the breast, and rarely in other clinical pictures as discharge, inflammatory changes or enlarged lymph node. Diagnosis is made by good anamnesis and diagnostic procedures (mammography, ultrasound, FNA*, biopsy). The disease is classified by TNM classification which determines further treatment and prognostic outcome. Treatment of breast cancer is carried out by surgical treatment, chemotherapy, radiotherapy, and hormonal therapy. Day clinic is the most common place of conducting chemotherapy. The role of the bachelor of nursing in the treatment of breast cancer is in the preparation and application of a chemotherapeutic agent and other drugs, the monitoring of vital parameters of the patient, keeping medical records of nursing and psychological support to the patient and family. Only a multidisciplinary approach to treating breast cancer can provide a better outcome of the disease.