HER2-positive breast cancer: update on Breast Cancer International Research Group trials.

HER2 gene amplification occurs in approximately 20% of primary breast cancers and is associated with a poor prognosis. Recently, trastuzumab, a humanized murine monoclonal antibody directed against the extracellular domain of HER2, was introduced for the treatment of patients with HER2-overexpressing advanced breast cancer. Trastuzumab has activity as both a single agent and in combination with chemotherapy. However, trastuzumab in conjunction with anthracyclines produces an unacceptably high rate of cardiac toxicity, which has prompted the search for alternative regimens. Docetaxel and the platinum salts are logical candidates to be combined with trastuzumab since these agents exhibit potent synergy with the antibody in preclinical experiments. Furthermore, the available phase II clinical data using the TCH (docetaxel/platinum/trastuzumab) regimen suggest this combination has significant activity. The Breast Cancer International Research Group (BCIRG) 006 trial is a 3-arm adjuvant study comparing doxorubicin/cyclophosphamide followed by docetaxel, the same regimen with trastuzumab administered with docetaxel (TH), and TCH in 3150 women with node-positive or high-risk node-negative, HER2-positive breast cancer. BCIRG 007 compares TH and TCH as first-line therapy in patients with HER2-positive metastatic breast cancer. In both trials, entry is restricted to patients whose tumors are positive for HER2 gene amplification as determined by fluorescence in situ hybridization. The data from these trials, in addition to the results from other ongoing randomized studies, will help define the optimal way to utilize trastuzumab in the management of patients with HER2-positive breast cancer.

Docetaxel in the treatment of breast cancer: an update on recent studies.

Recently there has been great interest in developing combination regimens involving taxanes and anthracyclines for the treatment of advanced breast cancer. Docetaxel in particular has substantial activity when combined with doxorubicin. In one randomized trial, the combination of doxorubicin 50 mg/m(2) and docetaxel 75 mg/m(2) showed significantly greater activity than doxorubicin plus cyclophosphamide (AC), producing a higher response rate (60% v 47%) and longer time to progression. In a second study, 484 patients were randomized to receive either docetaxel plus doxorubicin and cyclophosphamide (TAC) or 5-florouracil plus doxorubicin and cyclophosphamide. The response rate was significantly higher in the TAC arm (54% v 42%), including patients with unfavorable prognostic factors. Febrile neutropenia occurred more frequently in patients receiving TAC, but the incidence of infection and septic death was low and no greater than in the 5-florouracil/doxorubicin/cyclophosphamide arm. TAC was not associated with an increased risk of cardiotoxicity. Data on time to progression and survival are not yet available. The TAC and doxorubicin/docetaxel regimens have been compared with non-docetaxel-containing programs in randomized adjuvant trials which have completed accrual but are not yet mature. A second generation of adjuvant trials compares sequential versus synchronous docetaxel-based polychemotherapy. In addition, based on preclinical data suggesting a synergistic interaction between docetaxel, platinum salts, and trastuzumab, as well as preliminary data from pilot studies in patients with HER2-positive metastatic disease showing tolerability and activity, adjuvant studies of this novel three-agent combination are in progress in patients with HER2-positive early breast cancer.

Combined biological therapy of breast cancer using monoclonal antibodies directed against HER2/neu protein and vascular endothelial growth factor.

Vascular endothelial growth factor (VEGF) is one of the most important endothelial mitogens involved in the development and differentiation of the vascular system. Vascular endothelial growth factor is a highly conserved, homodimeric glycoprotein with multiple isoforms. The most abundant isoform, VEGF165, binds to vascular endothelial growth factor receptors-1 (Flt-1) and 2 (KDR/Flk-1) with picomolar affinity. Recently, correlation between microvessel density and engineered expression of VEGF in human breast xenografts was observed. A role of VEGF in breast cancer progression is evident from clinical studies showing elevated serum VEGF in invasive breast cancers. Vascular endothelial growth factor in breast tumor cytosols is correlated with microvessel density, and VEGF165 content correlates with disease-free and overall survival in primary breast cancers. Preliminary data indicate a transcriptional upregulation of VEGF in HER2-overexpressing breast cancer cells. We hypothesize that the upregulation of VEGF in HER2-overexpressing breast cancers contributes to the aggressive phenotype observed in HER2-positive cases and that the "angiogenic switch" associated with HER2 can be attenuated by trastuzumab. Although tumor angiogenesis in breast cancer is complex, the VEGF/vascular endothelial growth factor receptor (VEGFR) system provides a useful model for testing new angiogenesis inhibitors that target this pathway. The VEGF/VEGFR system provides a number of opportunities for therapeutic intervention in breast cancer. Understanding the biology of this system is paramount to fully exploiting VEGF as a therapeutic target in breast cancer. We hypothesize that new therapeutic molecules targeting VEGF and/or its receptors, such as recombinant humanized monoclonal anti-VEGF antibody (rhuMAb VEGF), may have unique activity against HER2-overexpressing breast cancers.

Combination chemotherapy for metastatic breast cancer.

Despite more than four decades of effort, the improvement in survival in metastatic breast cancer has been modest. Recently, however, new drugs such as the taxanes have emerged as pivotal agents in the treatment of metastatic disease and they are now being investigated in the adjuvant setting. In addition, the introduction of molecularly targeted therapies such as trastuzumab provides a new paradigm for the development of biologic treatments. The incorporation of trastuzumab into new combination regimens based on potential molecular synergies is a focus of current research.