Background. Gynecomastia is one of the most famous and common paraneoplastic syndromes. With the growth of equipment clinics with modern diagnostic equipment, including the CT, increases the detection of breast pathology in men. There is the need for a correct interpretation of the data about the state of male breast by radiologists, and the attending physician, oncologist, mammologist, urologist, endocrinologist.
 The purpose of the study to identify possible differences in frequency and radiation pattern of gynecomastia in patients with cancer and without it and also to follow the dynamics of the development of gynecomastia in patients with cancer, to identify the probable causes of the progression of gynecomastia in patients with cancer.
 Materials and methods. It's data of 400 chest CT of men who were screened and treated for the different oncological pathology in Voronezh regional clinical oncological hospital in 2013-2015. And also data of 150 chest CT of men who were screened and treated for the various diseases (excluding oncological diseases) in the Voronezh regional clinical diagnostic center and Kursk regional clinical hospital in 2013-2015 was used.
 Results. The data of the frequency of occurrence various types of gynecomastia in patients with cancer pathology and without it was obtained. The frequency of occurrence of gynecomastia in patients with cancer depending on the localization and morphology of tumor was analyzed. The dynamics of the gynecomastia in patients with cancer was tracked and possible causes of its progression in patients in this group were identified.
 Conclusions 1. Gynecomastia is a frequent pathology revealed by chest CT in men as suffering from oncological disease and without it.
 
 Gynecomastia significantly more often found in patients suffering from prostate adenocarcinoma and renal cell carcinoma.
 Surgical injury may be one of the reasons for the development of gynecomastia.
 Feature of gynecomastia in patients with cancer is its asymmetry. When the detection of asymmetrical gynecomastia by chest CT is recommend the further examination of patient to exclude him cancer pathology, special attention should be paid to the prostate gland and the kidneys.
 Upon detection of the progression of gynecomastia in a patient with a history of cancer need further examination to exclude cancer pathology progression.