ERBB2 and breast cancer: In addition, although trastuzumab exerts only modest complement-mediated cytotoxicity (CDC), a study of the CDC effect of the combination of trastuzumab and pertuzumab on HER-2-positive breast cancer cells showed that the suppression of complement regulatory factor expression by small interfering RNA increases the antitumor activity of trastuzumab and pertuzumab via complements and macrophages [41].