Clinicopathological Significance of HER2 Expression Redefined by the HER2-low Concept in Ductal Carcinoma In Situ

BACKGROUND/AIM: (DCIS) remains unclear. This study aimed to reassess HER2 expression in DCIS using the HER2-low classification. PATIENTS AND METHODS: A total of 221 patients who underwent surgery and were pathologically diagnosed with DCIS at Osaka Metropolitan University hospital between June 2007 and December 2023 were retrospectively analyzed. HER2 expression was assessed using immunohistochemistry (IHC) and classified as HER2-0, HER2-low (IHC 1-2+), or HER2-high (IHC 3+). Clinicopathological features were compared among groups, and disease-free survival (DFS) and recurrence-free interval (RFI) were evaluated using Kaplan-Meier and Cox regression analyses. RESULTS: =0.004). CONCLUSION: HER2 expression redefined by the HER2-low concept reflects the biological diversity of DCIS. Evaluation of HER2 status as a continuous spectrum may aid in risk stratification and contribute to understanding early HER2-driven tumor evolution.