<p>In this study, we analyzed the features of maturation of dendritic cell depending on the HER2 status of breast cancer based on morphology and immunophenotyping. Monocytes were isolated from the venous blood of 12 women with breast cancer: 4 patients with HER2^– status and 8 with HER2⁺ status. In patients with HER2^– status, significantly lower (<i>p</i> = 0.029) expression of costimulatory membrane signal CD86 on dendritic cells on day 9 of culturing and reduced (<i>p</i> = 0.03) number of stretched cells on day 2 of culturing were revealed. Additionally, a correlation (<i>r</i> = 510; <i>p</i> = 0.031) was found between HER2⁺ status and the number of round immature cells on day 7 of culturing. The results indicate that maturation of dendritic cells from peripheral blood monocytes from HER2⁺ status breast cancer patients is less active and incomplete on the first and last days in culture compared to cells from HER2^– patients. Low expression of CD86 costimulatory signal can be the cause of impaired antigen-presenting function of dendritic cells, which indirectly confirms aggressiveness of HER2⁺ breast cancer.</p>