Aims A high incidence of breast cancer is observed in all countries throughout the world, and this dictates the use of aggressive antitumor drugs. The toxogenic effect of anthracycline drugs on the cardiovascular system under conditions of oncological pathology determines the need to expand the diagnostic capabilities for detecting cardiotoxicity, including searching for signal morphological markers in blood serum. The aim of this work is to study the structure of solid-state films of blood serum in patients with breast cancer at the stages of their chemotherapeutic treatment to identify signal criteria for cardiotoxicity. Materials and methods Studies were conducted in 25 patients with primary breast cancer (BC) with an extent of spread of the tumor process corresponding to T2-4N0-1M0. Polychemotherapy (PCT) was carried out in a neoadjuvant regimen, which included doxorubicin (60 mg/m2) and cyclophosphamide (600 mg/m2) supported by echocardiography examinations and ECG monitoring. Morphological testing of solid-state blood serum samples was carried out using the Shatokhina-Shabalin method of wedge-shaped dehydration both before PCT and in the course thereof. Samples were visualized with the Leica DMLS2 microscope with a magnification from x20 to x90. Results Before starting the PCT course, in the serum facias, in 55% of the cases detected has been the loss of the radial symmetry system and the formation of pathological types, including the "double" facias that is a criterion of systemic intoxication. Local markers of comorbid states with a detection rate of up to 40% of intoxication, impaired vascular elasticity, sclerosis, hypertension and ischemia have been identified. After 3 courses of PCT including anthracyclines, the occurrence rate of formation of these pathological criteria increased by 1.7 times; the occurrence rate of myocardial trophic disorder markers was found to be higher. At stages 5-6 of the treatment course, in 80% of the cases, some signal signs of the cumulative effect of anthracyclines associated with impaired cardiac rhythmogenesis were detected in the facias structure. Conclusions Inhibition of tumor growth under PCT including anthracyclines is accompanied by structural deformation of the systemic and local self-organization of blood serum. An intensification of crystallogenesis of inflammation pathological proteins, sclerosis, intoxication, hypertension, stagnation angiospasm and cardiac arrhythmias makes it possible to assess the intensity of drug cardiotoxicity using the identifying markers, predict long-term effects of PCT and a possibility of their prevention.