DECODING HER2 LOW BREAST CANCERS: Impact on Diagnosis, Treatment, and Survivorship for Women in Aotearoa New Zealand

Intro: Pathological analysis of HER2 receptor levels in breast tumours guides systemic treatment options. Women with an amplified HER2 (ERBB2) gene in their tumour, as determined by +2/+3 immunohistochemical (IHC) staining and confirmed by FISH, can receive targeted therapies such as Trastuzumab. Tumours with +1/+2 IHC HER2 staining, initially considered HER2 negative, have led to the development of new drugs that capitalize on the presence of this receptor on breast cancer cells. These advancements have expanded treatment options for women with HER2 Low breast cancers, most importantly those with Advanced and Triple Negative Breast Cancers.

Our analysis, the first of its kind in Aotearoa, examines data from Te Rēhita Mate Ūtaetae to identify how many and which women would benefit from treatments targeted at HER2 low breast cancers.

Conclusion: HER2 low, an under-recognized subtype of breast cancer, demonstrates substantial therapeutic promise. Our data indicate that 35-40% of patients with advanced or triple-negative breast cancers in Aotearoa could be eligible for new targeted therapies. Although no such treatments are yet approved in New Zealand, they are available internationally. Future research is needed to evaluate the impact of these novel therapies on patient outcomes.