In this large-scale cross-sectional study, we evaluated disease-free survival (DFS), overall survival (OS), and clinicopathological characteristics of BC patients from 1991 to 2022, retrospectively. We recruited patients referred to the Cancer Research Center in Tehran, Iran, and their HER2 status, which is classified as HER2-low, HER2-positive, or HER2-negative, was obtained from prospectively maintained registries. we aimed to dive more deeply into the clinicopathological characteristics and survival features of HER2-low breast cancer patients and campared it with HER2-negative and HER2-positive groups.

Question 1: Is HER2-low breast cancer (BC) a new subtype in the standard classification of BCs? Question 2: How is the DFS and OS rate of HER2-low breast cancer patients in comparison with HER2-negative and HER2-positive groups?

Inclusion Criteria:

All breast cancer patients with human epidermal growth factor receptor 2 (HER2) status in the database of the Cancer Research Center (CRC),from April 1991 to March 2022

Exclusion Criteria:

The male gender Patients with indeterminate or missing HER2 status, or patients with missing DFS and OS information

The patients with male gender were excluded

There were 3918 patients with human epidermal growth factor receptor 2 (HER2) status in the database of the Cancer Research Center (CRC), among which, 24 male patients and 312 patients with missing DFS and OS information were excluded. In total, 3582 patients have been included in DFS and OS analysis.

Data will be available upon a reasonable request. Due to the sensitive nature of the clinical data collected in this study, patients were assured raw data would remain confidential and would not be shared except under specific requests.