Prospective cohort research to study the state of oxygen metabolism, reserve capabilities of cardiovascular and respiratory systems in patients with breast cancer to create a program of prevention and rehabilitation of lung damage in the process of complex treatment of the disease. The aim of the study is to study the dynamics of oxygen metabolism and reserve capabilities of cardiovascular and respiratory systems in the process of complex treatment of breast neoplasias. Objectives of the study: 1. Explore the dynamics of pulmonary ventilation and gas exchange disorders in patients with breast cancer in the course of radiation therapy 2. Establish an algorithm for risk stratification of post-radiation disorders of pulmonary ventilation and gas exchange in patients with breast cancer. 3. Analyze the prognostic significance of cardiopulmonary exercise testing in assessing the cardiotoxic effect of chemo- and radiation therapy in patients with breast cancer. 4. Analyze the influence of post-radiation disorders of pulmonary ventilation and gas exchange on the quality of life and psycho-emotional status of patients with breast cancer. 5. Develop a fundamental basis for the program of prevention and rehabilitation of post-radiation lung damage in patients with breast neoplasias based on the study of individual parameters of oxygen metabolism and reserve capabilities of cardiovascular and respiratory systems. All participants go through 5-week radiation therapy in standard protocol, will have investigation of their lung functioning by spirography and assessment of pulmonary diffusion capacity, cardiopulmonary stress tests and CT-scan on the lungs before radiotherapy course. Researchers will analyze such parameters as stage of the disease, surgery type, all patient's medications, complications, nutritional status, psychological status.