The article focuses on the influence of human leukemia differentiation factor (HLDF), carcinoembryonic antigen (CEA), and polyclonal activators (PA) on cytokine production by peripheral blood cells in breast cancer and benign breast diseases. It was found that the influence of internal factors on the production of cytokines by the peripheral blood cells is associated with lymphatic metastasis (CEA: IL-10; HLDF: IL-6, IL-1β, TNF-α, and G-CSF). One special circumstance was that there were no differences between the production of cytokines by peripheral blood cells in the patients with breast cancer compared to the patients with benign breast diseases with a high risk of malignant transformation. This is evidence of the functional similarity of peripheral blood cells in patients with these conditions. Cytokine production under the influence of PA was different only in case of TNF-α in all study groups.