Cancer is the second cause of death in Poland after cardiovascular diseases. The most frequently diagnosed cancer diseases in women are breast cancer and cervical cancer. Breast cancer is a significant medical and social problem both in Poland and in the world. Breast cancer significantly affects the emotional state of the patient, her self-esteem, as well as intimate, family and social relationships. The tasks of nurses taking care of breast cancer patients is to prepare for life in the changed health situation and to help the woman to be able to take care of herself to the highest possible degree. Dorothy Orem's theory of nursing diagnosis using the concepts of self-care and self-care deficit is important in the treatment of breast cancer. Also very important is psychological control, support from medical personnel and family environment. Breast cancer prevention is also important: self-control, i.e. palpation of the breast and screening tests. The paper contains a case report of nursing process in a patient suffering from breast cancer after mastectomy.