Introduction. In recent years, a separate publications have appeared indicating that interleukin 6 (IL-6) and the protein hepcidin 25 (GP25) play a significant role for the development of functional iron deficiency (FID) in oncological patients with a widespread tumor process. It is important to differentiate between FID and iron deficiency anemia (IDA), since they have the same morphological characteristics, but their treatment is fundamentally different.The aim of this study was to study the main metabolites of ferrokinetics, IL-6 and C-reactive protein (CRP) expression parameters in patients with breast cancer on the background of neoadjuvant chemotherapy to develop individual approaches to the diagnosis and treatment of anemic syndrome (AS), prediction, early detection of anemia and its adequate correction.Materials and methods. The study was conducted in 31 breast cancer patients, during of 6 cycles of chemotherapy. The main metabolites of ferrokinetics were studied: GP25, ferritin, soluble transferrin receptors, transferrin, iron, erythropoietin, IL-6 and CRP indices. The control group consisted of 29 apparently healthy women.Results. AS was detected in 14 (45.1 %) of breast cancer patients. IDA prevailed with microcytic, hypochromic characteristics of erythrocytes, a low concentration of ferritin, iron, GP25, IL-6, CRP, and a high level of transferrin and soluble transferrin receptors. A some patients were diagnosed with FID, mainly with the III and IV stages of the disease. Unlike IDA, they had a high concentration of ferritin, CRP and significant production of GP25, IL-6. Erythropoietin level was not optimal for the majority of patients with AS. A few patients on the background of treatment with recombinant erythropoietins revealed a deficiency of vitamins B12 (cyanocobalamin) and folic acid.Conclusion. Early diagnosis, a personalized approach to the prescription of iron preparations, recombinant erythropoietins, vitamins B12 and folic acid in patients with AS allowed for 6 cycles neoadjuvant chemotherapy without a significant decrease in erythrocytes, hemoglobin and hematocrit in most of them. The data obtained on IL-6, GP25, and CRP indicate relationship between them in the development of FID in breast cancer patients with a widespread tumor process and require further study.