Results of the deliberation on the reimbursement expansion of the new antibody-drug conjugate (ADC) Enhertu (trastuzumab deruxtecan) for HER2-low breast cancer and lung cancer are drawing attention.

According to industry sources, the Health Insurance Review and Assessment Service's Cancer Disease Deliberation Committee (CDDC) is scheduled to hold a meeting on the 30th to review 2 additional indications for Enhertu.

The indications under review are ▲HER2-low metastatic breast cancer and ▲HER2-mutated non-small cell lung cancer (NSCLC). If the reimbursement expansion is approved, this is expected to expand treatment access for breast cancer and lung cancer in Korea.

Both indications were approved by the Ministry of Food and Drug Safety in May last year based on the DESTINY-Breast04 and DESTINY-Lung02 clinical studies.

Notably, the trials demonstrated the efficacy of Enhertu in HER2-low breast cancer, where treatment options were previously for HER2-negative status patients, and marks the emergence of the first and only targeted therapy for HER2-mutated lung cancer.

Additionally, Enhertu has expanded its indication to include HER2 ultra-low expression in the United States by the FDA, suggesting its potential as a new standard treatment option for patients with metastatic breast cancer across the entire spectrum of HER2 expression, including HER2-positive, HER2-low, and HER2 ultra-low expression breast cancer.

The main point of the CDDC review was also focused on how to evaluate Enhertu's efficacy in HER2-low expression breast cancer, where existing HER2-targeted therapies have shown limited efficacy, despite the significant improvement in treatment outcomes for HER2-positive breast cancer achieved by existing HER2-targeted therapies.

Previously, HER2-positive breast cancer was defined as “HER2-positive if IHC 3+ or IHC 2+ and ISH-positive, and HER2-negative if IHC 0, IHC 1+, or IHC 2+ and ISH-negative.”

Joohyuk Sohn. Professor of Medical Oncology at Yonsei Cancer Center, said, “With the domestic approval of Enhertu's indication for HER2-low metastatic breast cancer, patients previously classified as HER2-negative with limited treatment options now have a new treatment option. This is expected to further improve the treatment landscape for HER2-positive metastatic breast cancer in Korea.”

Enhertu is the first anti-HER2 agent to demonstrate treatment benefits in HER2-low metastatic breast cancer, redefining the definition of HER2-low and presenting a new paradigm for metastatic breast cancer treatment.

Another key point is that patients with HER2-low breast cancer account for nearly half - approximately 45% to 55% - of all breast cancer patients. Additionally, HER2-low breast cancer accounts for approximately 60% of HER2-negative breast cancer cases.

Apart from the benefits of Enhertu, this means that the financial burden on health insurance due to the large number of patients would also likely need to be taken into consideration to a certain extent.

If reimbursement is expanded to include indications such as HER2-low breast cancer and HER2-mutated non-small cell lung cancer, this is expected to increase Enhertu’s insurance claims amount significantly. This is why there are industry views that the reimbursement expansion will depend on the financial sharing plan proposed by the pharmaceutical company.

However, when Enhertu was listed for reimbursement in Korea last April as a treatment for HER2-positive metastatic breast cancer and gastric cancer, the government had flexibly applied the ICER threshold to grant its reimbursement.

In March, Daiichi Sankyo reportedly applied for and held a drug briefing session on Enhertu’s use in HER2-mutated non-small cell lung cancer.

Drug information briefing sessions were introduced in 2010 to enhance the transparency and objectivity of evaluations by facilitating mutual sharing of information between pharmaceutical companies and reviewers regarding new drugs. Daiichi Sankyo also utilized this system during the initial approval of Enhertu.

Enhertu was jointly developed and commercialized by Daiichi Sankyo and AstraZeneca. In South Korea, it is co-developed and promoted by Daiichi Sankyo Korea and AstraZeneca Korea, with distribution handled by Daiichi Sankyo Korea.