The HER2-directed antibody–drug conjugate can be given to breast cancer patients with unresectable or metastatic HER2-low disease – defined as an immunohistochemistry score of 1+, or 2+ but with negative in situ hybridization – who have received prior chemotherapy in the metastatic setting or relapsed during or within 6 months of finishing adjuvant chemotherapy.
The decision follows the positive results of the phase 3 DESTINY-Breast04 trial that showed significantly improved progression-free and overall survival with T-DXd versus physician’s choice of single-agent chemotherapy in pretreated patients.
T-DXd has also received accelerated approval for previously treated patients with unresectable or metastatic NSCLC harboring activating HER2 mutations, as detected by an FDA-approved companion diagnostic, namely the plasma Guardant360® CDx (Guardant Health, Inc, Palo Alto, California, USA) and the tissue Oncomine™ Dx Target Test (Life Technologies Corporation, Carlsbad, California, USA).
The agency advises that “[i]f no mutation is detected in a plasma specimen, the tumor tissue should be tested.”
This approval is based on the phase 2 DESTINY-Lung02 study that showed promising efficacy of T-DXd in this patient population.
The recommended dose of T-DXd in the breast and lung cancer settings is 5.4 mg/kg every 3 weeks, to be given by intravenous infusion. T-DXd carries a Boxed Warning regarding the risk for interstitial lung disease and embryo–fetal toxicity.
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