In vitro effects of trastuzumab and vinorelbine in trastuzumab-resistant breast cancer cells

Purpose. The majority of patients who initially respond to trastuzumab will progress within 1 year. Currently, patients who progress after trastuzumab-based therapy are often maintained on trastuzumab combined with a different chemotherapeutic agent, such as vinorelbine. However, evidence supporting the continued use of trastuzumab in these breast cancers is lacking. Methods. We created a preclinical model of trastuzumab resistance using the SKBR3 HER-2-overexpressing breast cancer cell line. Dose-response and cell cycle alterations in response to trastuzumab and/or vinorelbine were assessed. Results. In contrast to the parental SKBR3 cells, vinorelbine-mediated growth inhibition and apoptosis were not significantly enhanced by the addition of trastuzumab in the trastuzumab-resistant pools. Conclusions. These results suggest that the continued treatment of trastuzumab-resistant breast cancers with trastuzumab-containing regimens may not be effective. A randomized clinical trial of trastuzumab plus vinorelbine versus vinorelbine alone should be conducted in patients with HER-2-overexpressing breast cancer to determine the optimal duration of trastuzumab therapy upon progression.