Targeted Therapy for HER2-Low Breast Cancer Gets FDA OK

The US FDA has approved Enhertu (fam-trastuzumab-deruxtecan-nxki), an IV infusion for the treatment of patients with unresectable (unable to be removed) or metastatic (spread to other parts of the body) HER2-low breast cancer. This is the first approved therapy targeted to patients with the HER2-low breast cancer subtype, which is a newly defined subset of HER2-negative breast cancer.

It is estimated that 287,850 new cases of female breast cancer will be diagnosed in 2022 in the US. Approximately 80-85% of those new cases were previously considered to be HER2-negative subtype (including hormone receptor positive and triple negative breast cancer), which means the tumors do not overexpress, or make too many copies of the HER2 protein. Of that proportion of breast cancer diagnoses, about 60% of patients previously classified as having HER2-negative subtype can now be considered as HER2-low. Prior to today's approval, HER2-low patients received endocrine therapy or chemotherapy.

"Today's approval highlights the FDA's commitment to be at the forefront of scientific advances, making targeted cancer treatment options available for more patients," said Richard Pazdur, MD, director of the FDA's Oncology Center of Excellence and acting director of the Office of Oncologic Diseases in the FDA's Center for Drug Evaluation and Research. "Having therapies that are specially tailored to each patient's cancer subtype is a priority to ensure access to safe and innovative treatments."

As part of the Administration's Cancer Moonshot program, President Biden tapped federal agencies to develop ways to reduce the rate of cancer deaths and improve the lives of cancer patients and their families through advancements in cancer research and technology, and development of new programs. Enhertu's approval further illustrates how the FDA's efforts align with the Cancer Moonshot goals of targeting the right treatments to the right patients, speeding progress against the most deadly and rare cancers, and learning from the experience of all patients.

HER2 receptors, which are proteins made by the HER2 gene, are important in determining a patient's treatment. HER2-negative includes hormone receptor positive and triple negative breast cancers. HER2-low is a new classification of the HER2 subtype. It describes a new subtype of breast cancer that has some HER2 proteins on the cell surface, but not enough to be classified as HER2-positive.

Patients with HER2-low breast cancer are eligible for Enhertu if they have received a prior chemotherapy in the metastatic setting, or their cancer returned during, or within 6 months of completing, adjuvant chemotherapy.

This approval is based on DESTINY-Breast04, a randomized, multicenter, open label clinical trial that enrolled 557 adult patients with unresectable or metastatic HER2-low breast cancer. The trial included two cohorts: 494 hormone receptor positive (HR+) patients and 63 hormone receptor negative (HR-) patients. Of these patients, 373 randomly received Enhertu by intravenous infusion every three weeks and 184 randomly received physician's choice of chemotherapy (eribulin, capecitabine, gemcitabine, nab paclitaxel or paclitaxel). The results showed improvement in both progression-free survival and overall survival in people with unresectable or metastatic HER2-low breast cancer.

The median age of trial participants was 57 years old, ranging from 28 to 81 years of age. Among the 557 patients, 24% were age 65 or older. Females comprised 99.6% of the trial population. Trial participants' race was reported as 48% White, 40% Asian, 2% Black or African American, and 3.8%Hispanic/Latino.

The most common adverse reactions in patients receiving Enhertu in DESTINY-Breast04 are nausea, fatigue, alopecia, vomiting, constipation, decreased appetite, musculoskeletal pain and diarrhea. The prescribing information includes a boxed warning to advise health care professionals of the risk of interstitial lung disease and embryo-fetal toxicity. Enhertu is not recommended for women who are pregnant.

Enhertu received priority review and breakthrough therapy designations for this indication. The FDA granted the approval of Enhertu to Daiichi Sankyo four months ahead of the Prescription Drug User Fee Act (PDUFA) deadline.