Earlier studies in which the nonspecific immunostimulants bacille Calmette-Guerin or levamisole were added to chemotherapy showed no advantage to this procedure. In the last 2

years, however, studies using specific immunotherapy with the humanized murine monoclonal antibody trastuzumab have yielded promising results. This antibody recognizes and binds to a transmembrane tyrosine kinase coded for by the c-erbB2 or HER2 gene, which is amplified and/or overexpressed in up to one-third of all breast cancer specimens (Figure 17-2). When given to a heavily pretreated group of patients whose tumors overexpressed this gene product, trastuzumab produced a 16 percent objective response rate.81 Toxicity was minimal, consisting of fever and chills after the first weekly infusion, and mild pain, asthenia, nausea, diarrhea, and dyspnea. In addition, 5 percent of patients had evidence of cardiac dysfunction.

Trastuzumab was also studied in a placebo-controlled study involving women simultaneously receiving chemotherapy with either dox-orubicin-cyclophosphamide or paclitaxel.82 When added to doxorubicin-cyclophosphamide, the response rate increased from 43 to 52 percent, with a 3.6-month prolongation of responses. When trastuzumab was added to paclitaxel in patients who had prior exposure to doxorubicin, response rate increased from 16 to 42 percent, and duration of response from 4.4 to 11 months. Unfortunately, cardiotoxicity was seen in 27 percent of women receiving the doxorubicin combi-

Figure 17-2. A breast cancer showing overexpression of membrane associated HER-2 protein. Metastatic breast cancer with this phenotype demonstrates a 16% response rate to trastuzumab when employed as a single agent.

nation plus antibody treatment and in 12 percent receiving paclitaxel plus antibody. The mechanism of this synergy, manifest both in increased response rates and cardiotoxicity, is not yet understood, and a wide variety of trials have begun to define the role of trastuzumab in the treatment of metastatic breast cancer.

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