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Background: Preclinical data indicate that docetaxel, platinum salts, and the combination of both drugs are highly synergistic with the anti-HER2 antibody trastuzumab. The University of California at Los Angeles-Oncology Research Network (UCLA-ORN) and the Breast Cancer International Research Group (BCIRG) have conducted two phase II studies to evaluate docetaxel and trastuzumab in combination with either cisplatin or carboplatin for the treatment of women with advanced breast cancer that overexpresses HER2. Methods: Each study enrolled 62 patients with HER2-overexpressing tumors. Patients received a median of six cycles of docetaxel at 75 mg/m 2 of body surface area and cisplatin (BCIRG 101 study) at 75 mg/m 2 or carboplatin (UCLA-ORN study) at AUC 6 mg/mL ·min given on day 1 and then every 21 days. Trastuzumab was given on day 1, cycle 1 (4 mg/kg) and then continued weekly at 2 mg/kg for 1 year or until disease progression. Tumor measurements were obtained at baseline, after three cycles of chemotherapy, and then every 3 months. HER2 gene amplification was determined by fluorescence in situ hybridization. Results: Patient characteristics were comparable between trials with the exception that 15% of the patients in the UCLAORN study had received previous adjuvant taxane therapy. Both regimens were well tolerated, with manageable toxicities. Hematologic toxicities were more frequent in patients in the UCLA-ORN study than in patients in the BCIRG 101 study, whereas the reverse pattern was observed for non-hematologic toxicities. One patient in each study developed reversible congestive heart failure. Responses were observed in 49 of 62 patients in the BCIRG 101 study (overall response rate 79%, 95% confidence interval [CI] 66% to 89%) and in 34 of 59 evaluable patients in the UCLA-ORN study (overall response rate 58%, 95% CI 44% to 70%). Median times to progression were 9.9 months (95% CI 8.3 to 13.1 months) and 12.7 months (95% CI 8.6 to 15.5 months) for patients in the BCIRG 101 and UCLA-ORN studies, respectively. Overall response rates were higher and median time to progression was longer in the subset of patients whose tumors harbored HER2 gene amplification. Conclusion: Combinations of docetaxel, a platinum salt, and trastuzumab are feasible and active in patients with advanced breast cancers that overexpress HER2. The BCIRG is conducting ongoing randomized studies of the three-drug combination in both the metastatic and adjuvant settings. [J Natl Cancer Inst 2004;96:759 ‐69]

Background: Trastuzumab, a humanized anti-HER2 antibody, increases the clinical benefit of first-line chemotherapy in patients with metastatic breast cancers that overexpress HER2. We characterized interactions between trastuzumab and chemotherapeutic agents commonly used in the treatment of breast cancer. Methods: Multiple drug effect/combination index isobologram analysis was used to study the efficacy of chemotherapeutic drug plus trastuzumab combinations tested against four HER2-overexpressing breast cancer cell lines (SK-BR-3, BT-474, MDA-MB-361, and MDAMB-453). Combination index values were derived from parameters of the median effect plots, and statistical tests were used to determine whether the mean combination index values at multiple effect levels were statistically significantly different from a combination index value of 1.0. Values less than 1.0 indicate synergistic interactions, values greater than 1.0 indicate antagonistic interactions, and values equal to 1.0 indicate additive interactions. Results: At a wide range of clinically achievable drug concentrations, synergistic interactions were observed in all four breast cancer cell lines for trastuzumab plus carboplatin (mean combination index values ranged from 0.32 [P