Each year, October marks National Breast Cancer Awareness Month, an event established to support awareness, prevention, and continued research. In addition to the month-long period, by unanimous House and Senate resolution in 2009, October 13th became a day devoted to metastatic breast cancer awareness. New, practice-changing approvals for a targeted therapy and companion diagnostic for patients with HER2-low metastatic breast cancer add poignancy to these health campaigns, bringing hope to patients whose outcomes may improve following the recent innovations.

New cases of breast cancer being diagnosed throughout 2022 are estimated to number over 290,000, and deaths are estimated to be nearly 44,000. In the earliest stages, when the cancer remains limited to the breast tissue, patients have a 99% 5-year survival rate. For many, breast cancer may infiltrate other tissues and systems, and this metastasis will require careful, strategic treatment approaches to help control and treat the disease and help prolong patient life. Biomarking testing will be used to determine which, if any, kinds of receptors are present on breast cancer cells. When the breast cancer cells are found to have above-normal numbers of HER2 receptors, the cancers are referred to as HER2-positive. If there is minimal or no HER2 expression, then the classification has generally been HER2-negative. Today there is a newly defined and significant subtype that consists of tumors expressing a minimal amount of HER2 receptors, now referred to as HER2-low. This group has been determined to represent over half of all metastatic breast cancers.

Based on impressive efficacy outcomes through clinical trials, Enhertu (fam-trastuzumab deruxtecan-nxki) for injection, for intravenous use was approved in August 2022 for use in adult patients with unresectable or metastatic HER2-low breast cancer who have received a prior chemotherapy in the metastatic setting or developed disease recurrence during or within six months of completing adjuvant chemotherapy. It is the first time a targeted therapy has received approval for the new subtype. The antibody-drug complex is designed to allow a trastuzumab biosimilar to attach to HER2 proteins, thereby preventing growth, while carrying the topoisomerase I chemotherapy component that works to stop cancer cell replication. The trials for Enhertu have attributed remarkable outcomes for the medication. Results included a 50% reduction in the risk of disease recurrence or death. Patients who have not had success with previous targeted medications might benefit from the directed therapy made possible with Enhertu. It would be additionally advantageous for patients previously considered to be HER2-negative to investigate with their healthcare providers if reclassification as HER2-low is appropriate. Healthcare teams treating breast cancer patients will benefit from the companion test approved in October 2022 that is able to identify patients for whom Enhertu is a treatment option. According to its manufacturer, the PATHWAY anti-HER2/neu (4B5) rabbit monoclonal primary antibody test has been enhanced with a scoring algorithm designed for identification of low expression of HER2, which allows assignment of HER2-low status.

Advancements like the treatment potential of Enhertu for HER2-low breast cancer reinforce the benefit of testing to identify patients who are candidates for targeted therapy. As guidelines and further approvals are achieved after continued research and understanding of long-term results, exciting advances in related targeted therapy will continue. Stay informed about emergent drug information, including treatment options for metastatic breast cancer, by updating or registering your profile to receive email alerts and other critical drug information updates from PDR. You can also stay current by using the official PDR app, mobilePDR, available for free from your favorite app stores.