Breast cancer (BC) is the most prevalent cancer and the first leading cause of cancer death in women in Tunisia, with an estimated 3092 new cases and 986 deaths from cancer in 2020 [1]. Around 5 % of women diagnosed with invasive BC have synchronous metastases, while 20 % of those with early stage BC will develop metastatic disease. In both the early and metastatic phases, immunohistochemical analysis of three key biomarkers: estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2), determines treatment plan and prognosis [2]. The status of these biomarkers in primary breast carcinomas (PBC) and their corresponding distant metastases has been found in several reports to differ significantly [2], [3], [4], [5], [6], [7]. In the literature, there is a considerable range in the frequency of these biomarker status changes [2], [3], [4], [5], [6], [7]. However, the prognostic impact of these changes remains unclear.

In light of this, this study aimed to compare ER, PR, and HER2 expression in PBC and their matched metastatic lesions, search for factors associated with biomarker status discordance, and assess the impact of potential biomarker status discordance on patient outcome.