Introduction: According to the literature (1-3), systemic autoimmune diseases are associated with an increased risk of developing malignant diseases. This risk arises from the immune effects of autoimmune combined with drug treatment for autoimmune disease.

Case report: This case shows a 51-year-old female patient who presented with dyspnea and exercise intolerance in last two weeks, with medical history of long-term treated hypertension and autoimmune diseases: thyreopathy and overlap syndrome. During cardiological assessment transthoracic echocardiography showed large tumor formation that filled left atrium and protruded to the left ventricle in diastole, which was confirmed by transesophageal echocardiography and thoracic CT. After complete cardiological treatment, the patient was successfully operated at the Department of Cardiac Surgery. PHD report confirmed diagnosis of myxoma. It was the most important since the most common intracardiac formations are primary (benign or malignant) tumors, metastatic tumors, thrombus or vegetation. Although there is no clear connection between autoimmune diseases and benign tumors, it is interesting to see significant reduction of immune markers in laboratory labs (especially CCP) following surgery.