Analysis of HER2-Low Breast Cancer in Aotearoa New Zealand: A Nationwide Retrospective Cohort Study.

Simple Summary: This research is the first comprehensive study in New Zealand to categorise and examine the characteristics of breast cancer based on HER2 status. We explored three HER2 categories: HER2-zero, HER2-low, and HER2-positive, in women diagnosed with invasive breast cancer. Utilising Te Rēhita Mate Ūtaetae (Breast Cancer Foundation NZ National Register), our study analysed data spanning 21 years, revealing that most women underwent HER2 testing. Significantly, many cases previously not recognised as having significant HER2 levels were in fact HER2-low, qualifying them for newer, targeted drug therapies. These findings are particularly crucial as they suggest that newer therapies could benefit a larger segment of patients, notably those with advanced breast cancer; approximately 60% of these women might now benefit from these innovative HER2-targeted treatments. The study underscores the urgent need for standardised HER2 testing to personalise and optimise treatment, enhancing outcomes for patients with invasive breast cancer. Objectives: To perform the first national analysis of demographic and clinicopathological features associated with the HER2 positive, HER2-low, and HER2-zero invasive breast cancers in New Zealand. The study will reveal the proportion of women who may benefit from new HER2-targeted antibody drug conjugate (ADC) therapies. Methods: Utilising data from Te Rēhita Mate Ūtaetae (Breast Cancer Foundation NZ National Register), the study analysed data from women diagnosed with invasive breast cancer over a 21-year period. The HER2 status of tumours was classified into three categories—HER2-zero, HER2-low, HER2-positive. Results: From 2009–2021, 94% of women underwent HER2 testing, with 14% diagnosed with HER2-positive breast cancer. For advanced-stage disease, 38% of those formerly classified as HER2-negative were reclassified as HER2-low. Including HER2-positive breast cancers, this indicates that 60% of women with advanced breast cancer may potentially benefit from the new HER2-directed ADCs (approximately 120 women per year). Conclusions: The findings suggest a significant proportion of women with invasive breast cancer in New Zealand could benefit from new HER2-targeted treatments. There is a need to standardise HER2 testing to enhance personalised treatment and improve outcomes. [ABSTRACT FROM AUTHOR]