HER2 Expression and Axillary Metastasis in Treatment-Naïve Early Breast Cancer

Area of Science:

• Oncology
• Breast Cancer Research
• Molecular Diagnostics

Background:

• The clinical significance of HER2-low breast cancer, especially in early-stage, treatment-naïve patients, is debated.
• Neoadjuvant therapy can alter tumor biology and nodal status, necessitating evaluation of upfront surgery cohorts.
• The HER2-ultralow subgroup's impact on axillary metastasis requires investigation.

Purpose of the Study:

• To evaluate the association between HER2 expression (including HER2-ultralow) and axillary metastasis in hormone receptor-positive, early-stage breast cancer patients.
• To determine if HER2 status predicts sentinel lymph node (SLN) positivity in treatment-naïve patients.
• To identify predictors of axillary metastasis in this cohort.

Main Methods:

• Retrospective analysis of 407 hormone receptor-positive, early-stage breast cancer patients undergoing upfront surgery (2017-2023).
• Categorization into HER2-ultralow (IHC 0), HER2-low (IHC 1+ or 2+/FISH-negative), and HER2-positive (IHC 3+ or 2+/FISH-positive) groups.
• Comparison of SLN positivity rates and multivariable logistic regression/ROC analyses for metastasis predictors.

Main Results:

• Similar SLN positivity rates across HER2-ultralow (29.0%), HER2-low (30.6%), and HER2-positive (31.3%) groups.
• HER2 expression was not an independent predictor of SLN positivity.
• Lymphovascular invasion (LVI) was the strongest determinant of axillary metastasis (OR=5.42), followed by tumor size and proliferative activity.

Conclusions:

• HER2 expression is not independently associated with axillary metastasis risk in treatment-naïve, early-stage breast cancer patients undergoing upfront surgery.
• Lymphovascular invasion, tumor size, and proliferative activity are the primary determinants of axillary involvement.
• Further research with longer follow-up is needed to confirm survival differences.