Introduction

The recently highlighted HER2 low breast cancer (BC) subgroup (IHC 1+ or IHC ‎‎2+/ISH ‎negative) has challenged the established binary categorization of BC into ‎HER2 ‎overexpressing tumors and HER2 negative. This raises the question of ‎whether the HER2 ‎low status influences disease phenotype in a manner similar to ‎HER2 overexpression.‎
‎ Aim
To Identify the prevalence of low HER-2 status among non-metastatic BC ‎patients in ‎comparison to HER-2 negative and HER-2 positive, and to compare ‎treatment outcome of ‎HER-2 low to HER-2 negative non-metastatic BC. ‎

Patients and methods
This retrospective study of 1029 early BC patients diagnosed between 2014 and ‎‎2022 in ‎Alexandria university hospitals. Tumors originally reported as HER2 ‎negative were ‎recategorized into HER2 0 and HER2 low based on the results of ‎IHC and FISH. HER2 low ‎and HER2 positive groups were compared to HER2-‎‎0 in terms of clinical and pathological ‎features.‎
Results
‎192 (18.7%) patients were HER2 positive, 779 (75.7%) were reported as HER2 ‎negative, and ‎were reclassified into 441 (56%) HER2-0, and 338 (43%) HER2 ‎low. 58 (5.6%) patients with ‎undetermined HER2 status were excluded.‎