Our study aimed to assess the changes in immunohistochemistry biomarker status (estrogen receptor [ER], progesterone receptor [PR], and human epidermal growth factor receptor 2 [HER2]) in BC cells after administration of NACT at a single institution in Oman.<h4>Methods</h4>We conducted a retrospective cross-sectional study on patients with BC with residual disease post-NACT in a single institution and studied immunohistochemistry status changes before and after NACT. This evidence concerns the gene ESR1 and breast cancer.