FIELD : biotechnology.SUBSTANCE : invention refers to medicine and biotechnology, particularly to determining the proliferative activity of tumor cells of triple-negative breast cancer. Method involves preparation of paraffin blocks from tumor tissue and histological sections, their dewaxing in hexane. Uncoloured dewaxed histological sections of tumor tissue are subjected to fluorimetric analysis and fluorescence excitation spectra are measured from 230 to 360 nm at a detection wavelength of 410 nm and fluorescence spectra at excitation wavelength of 300?nm and detection wavelength from 330 to 450 nm, determining the ratio between intensities of curves with maxima in region of 265 and 305 nm (I265/I305), and if I265/I305 = 1.0, the proliferative activity is low, the ratio I265/I305 indicates high proliferative activity.EFFECT : invention increases efficiency of obtained results.1 cl, 3 dwg, 1 tbl, 4 ex