HER2-Low Metastatic Breast Cancer - Tumour Deck

The current clinical definition of HER2-low Breast Cancer (HER2-Low BC) used in clinical practice and ongoing clinical trials relies on the standard IHC and ISH approach; thus, tumors with low level of HER2 expression (defined as a HER2 IHC score of 1+ or 2+) and no detectable ERBB2 amplification fall into this category. It is a newly defined subset of HER2-negative BC that has HER2 immunohistochemical (IHC) score of 1+ or score of 2+/in situ hybridization (ISH) negative phenotype. IHC/ISH is the only standard technique currently applied to define HER2 expression.

"The treatment armamentarium for HER2-low metastatic breast cancer is rapidly evolving. Recent clinical trials have demonstrated the efficacy of CDK4/6 inhibitors in combination with endocrine therapy as a standard first-line treatment option. Additionally, the use of PI3K inhibitors and AKT inhibitors is being explored in clinical trials and may provide further treatment options in the near future."

HER2 low metastatic breast cancer is a new subtype of breast cancer which accounts for approximately 50%-60% of newly diagnosed breast cancer cases. This indicates that HER2 low breast cancer is a relatively common subtype of the disease. Even though HER2-low breast cancer has some HER2 expression, it is generally considered and treated as HER2 negative. Studies have shown that HER2-low expression is more common in HR+ breast cancer, but it can also be found in HR negative breast cancer (Won et al., 2021; Tan et al., 2021).

Mellalta Meets HER2-Low Expression in Breast Cancer: Evaluating the Evidence, Challenges, and Opportunities for Expanding Treatment Benefit to More Patients

Mellalta's HER2-Low Metastatic Breast Cancer Deck: Current Treatment Landscape

Currently the mainstay of treatment for HER2-Low Metastatic Breast Cancer consist of combination of different therapeutic approaches like chemotherapy, endocrine therapies, targeted therapies.

In recent years, targeted therapies have shown promise in clinical trials and are being explored as alternative treatment options. The current standard of care for HER2-low metastatic breast cancer is rapidly evolving due to recent advancements in targeted therapies. Recent clinical trials have demonstrated significant clinical benefits of novel HER2-directed antibody-drug conjugates (ADCs) in treating HER2-low tumors. One such approved ADC is trastuzumab deruxtecan (T-Dxd), which has shown promising results in HER2-low breast cancer.

In addition to targeted therapies, endocrine therapy is also an important treatment option for HER2-low breast cancer, particularly in patients with hormone receptor-positive disease. Combination therapies, such as CDK4/6 inhibitors in combination with endocrine therapy, have also shown promise in improving outcomes for patients with HER2-low breast cancer.

"It is exciting that we have been able to now translate HER2-targeted therapy to a broader group of patients with HER2-low-expressing breast cancer. Overall, promising responses to T-DXd offer newfound treatment possibilities for a substantial number of patients, many of whom were previously considered to have limited therapeutic options. The recognition of HER2-low status also signals an opportunity to develop more precise, individualized therapeutic approaches through future research."

Mellalta's HER2-Low Metastatic Breast Cancer Deck: Current Unmet Needs

• Need for a clear and universally accepted definition of HER2-low, as the current classification is still evolving and there is ongoing research to determine the minimum threshold of HER2 expression required for treatment efficacy.

• HER2-low breast cancer (BC) has a poor prognosis, making the development of more suitable treatment an unmet clinical need.

• Need for standardized diagnostic criteria and guidelines for HER2-low tumors.

• Limited options for combination therapies that can enhance the efficacy of HER2-targeted treatments in HER2-low tumours.

"We are facing real challenges in terms of [HER2] identification in the clinic, and I would contend that we are in a state of flux in terms of the identification."

Mellalta's HER2-Low Metastatic Breast Cancer Deck: Key Takeaways

• Human epidermal growth factor receptor 2 (HER2) breast cancer, especially in the unresected, metastatic setting, is no longer considered solely binary as positive or negative.

• There is a new generation of approved antibody drug conjugate (ADC) like Trastuzumab deruxtecan (T-DXd) that have a higher drug-to-antibody ratio (DAR) and can deliver the toxin in a more effective manner for advanced unresectable, metastatic breast cancer.

• The 2023 National Comprehensive Cancer Network (NCCN) guidelines for the use of trastuzumab deruxtecan (T-DXd) reflect the clinical trial eligibility for DESTINY-Breast04. This allows health care professionals to use other ADCs approved for hormone receptor (HR)-positive and triple negative disease, irrespective of HER2 status.

• A traditional immunohistochemical (IHC) assay and scoring system have been used in testing to identify HER2-low tumors and the tumors with an IHC score of more than 0, less than 1+. New technologies may help to better identify patients with this subtype of tumor.

• The recently presented data of the DAISY trial suggested meaningful activity of T-DXd even in patients with HER2-0 metastatic breast cancer

Mellalta's HER2-Low Metastatic Breast Cancer Deck: Questions Answered:

• Potential challenges and opportunities in implementing targeted therapies for HER2-low breast cancer

• What is the size of clinically and commercially relevant drug-treatable HER2 low BC populations, and how will drug-treatment rates change over time?

• What is the expected market impact of recent drug approval such as Enhertu in treatment landscape of HER2-low metastatic BC?

• What are the most promising agents in the pipeline, and how will they shape the future of this therapy market?

• What key drivers and constraints will affect the HER2 low metastatic breast cancer therapy market over the forecast period?