Expanded PBS Listing for Trastuzumab Deruxtecan

The Pharmaceutical Benefits Scheme (PBS) listing for trastuzumab deruxtecan has recently been expanded to include human epidermal growth factor receptor 2 (HER2)-low unresectable or metastatic breast cancer.

Breast cancer patients have historically been classified as HER2-positive or HER2-negative. Up to 20% of breast cancers are classified as HER2-positive, and these patients can be treated with HER2-targeted therapies, such as trastuzumab deruxtecan. While HER2-negative cancers are not treated with these therapies, more than half of breast cancers have low levels of HER2 expression and may still be targetable with trastuzumab deruxtecan.

The DESTINY-Breast04 study was conducted in patients with previously treated HER2-low metastatic breast cancer. Patients were randomly assigned to receive trastuzumab deruxtecan or the physician’s choice of chemotherapy. The median progression-free survival (PFS) was 9.9 months in the trastuzumab deruxtecan group and 5.1 months in the physician’s choice group; overall survival was 23.4 months and 16.8 months, respectively. The majority of patients (88.7%) had hormone receptor-positive disease. In this cohort, the median PFS was 10.1 months in the trastuzumab deruxtecan group and 5.4 months in the physician’s choice group; overall survival was 23.9 months and 17.5 months, respectively.

The safety profile of trastuzumab deruxtecan in this population was consistent with that seen in previous studies. Interstitial lung disease, pneumonitis, reduced left ventricular ejection fraction, and neutropenia have been associated with trastuzumab deruxtecan. Patients should have their complete blood count monitored and counselled to seek medical advice if they experience any new or worsening respiratory or cardiovascular symptoms.