PURPOSE Trastuzumab deruxtecan (T-DXd, formerly DS-8201a) is a novel human epidermal growth factor receptor 2 (HER2)-targeted antibody drug conjugate (ADC) with a topoisomerase I inhibitor payload. A dose escalation and expansion phase I study evaluated the safety and activity of T-DXd in patients with advanced HER2-expressing/mutated solid tumors. Here, results for T-DXd at the recommended doses for expansion (RDE) in patients with HER2-low (immunohistochemistry [IHC] 1+ or IHC 2+/in situ hybridization−) breast cancer (ClinicalTrials.gov identifier: NCT02564900 ) are reported. PATIENTS AND METHODS Eligible patients had advanced/metastatic HER2-low–expressing breast cancer refractory to standard therapies. The RDE of 5.4 or 6.4 mg/kg T-DXd were administered intravenously once every 3 weeks until withdrawal of consent, unacceptable toxicity, or progressive disease. Antitumor activity and safety were assessed. RESULTS Between August 2016 and August 2018, 54 patients were enrolled and received ≥ 1 dose of T-DXd at the RDE. Patients were extensively pretreated (median, 7.5 prior therapies). The confirmed objective response rate by independent central review was 20/54 (37.0%; 95% CI, 24.3% to 51.3%) with median duration of response of 10.4 months (95% CI, 8.8 month to not evaluable). Most patients (53/54; 98.1%) experienced ≥ 1 treatment-emergent adverse event (TEAE; grade ≥ 3; 34/54; 63.0%). Common (≥ 5%) grade ≥ 3 TEAEs included decreases in neutrophil, platelet, and WBC counts; anemia; hypokalemia; AST increase; decreased appetite; and diarrhea. Three patients treated at 6.4 mg/kg suffered fatal events associated with T-DXd–induced interstitial lung disease (ILD)/pneumonitis as determined by an independent adjudication committee. CONCLUSION The novel HER2-targeted ADC, T-DXd, demonstrated promising preliminary antitumor activity in patients with HER2-low breast cancer. Most toxicities were GI or hematologic in nature. ILD is an important identified risk and should be monitored closely and proactively managed.

Purpose We compared nab-paclitaxel or ixabepilone once per week to paclitaxel with bevacizumab as first-line therapy for patients with advanced breast cancer (BC) to evaluate progression-free survival (PFS) for nab-paclitaxel or ixabepilone versus paclitaxel. Patients and Methods Eligible patients were age ≥ 18 years with chemotherapy-naive advanced BC. Patients were randomly assigned to bevacizumab with paclitaxel 90 mg/m2 (arm A), nab-paclitaxel 150 mg/m2 (arm B), or ixabepilone 16 mg/m2 (arm C), once per week for 3 of 4 weeks. Planned enrollment was 900 patients, which would give 88% power to detect a hazard ratio of 0.73. Results In all, 799 patients were enrolled, and 783 received treatment (97% received bevacizumab). Arm C was closed for futility at the first interim analysis (n = 241), and arm A (n = 267) and arm B (n = 275) were closed for futility at the second interim analysis. Median PFS for paclitaxel was 11 months, ixabepilone was inferior to paclitaxel (PFS, 7.4 months; hazard ratio, 1.59; 95% CI, 1.31 to 1.93; P < .001), and nab-paclitaxel was not superior to paclitaxel (PFS, 9.3 months; hazard ratio, 1.20; 95% CI, 1.00 to 1.45; P = .054). Results were concordant with overall survival; time to treatment failure was significantly shorter in both experimental arms v paclitaxel. Hematologic and nonhematologic toxicity, including peripheral neuropathy, was increased with nab-paclitaxel, with more frequent and earlier dose reductions. Conclusion In patients with chemotherapy-naive advanced BC, ixabepilone once per week was inferior to paclitaxel, and nab-paclitaxel was not superior with a trend toward inferiority. Toxicity was increased in the experimental arms, particularly for nab-paclitaxel. Paclitaxel once per week remains the preferred palliative chemotherapy in this setting.