Our measurements revealed that the increasing the concentrations of the C1q and C3 resulted in the statistically significant increase in the efficacy of the HER-2+ OV-90, TOV-112D, and OVCAR-3, and the patients’ epithelial ovarian cancer (EOC) cells killing by AVEC, trastuzumab, and anti-HER-2 biosimilar antibodies as compared to labeling with the isotype antibodies. Here, C3 is linked to ovarian carcinoma.