Discrepancy in the expression of ER, PR, HER2 receptors and the Ki-67 marker between the primary tumor and recurrence of breast cancer

Objective: To study changes in the expression of estrogen receptors (ER), progesterone receptors (PR), human epidermal growth factor 2 (HER2) and the proliferative marker Ki-67 between primary tumors and recurrent/metastatic lesions in patients with breast cancer. Materials and Methods: A prospective analysis of data from 42 patients with recurrent breast cancer followed at the Republican Oncology Research Center of the Ministry of Health and Social Development of the Republic of Tajikistan (2018-2024) was conducted. All patients underwent immunohistochemistry (IHC) testing of both the primary tumor and the recurrent or metastatic lesion. ER, PR, HER2 status, and Ki-67 levels were compared between paired samples. Results: The data demonstrated statistically significant discordance in biomarker expression. The proportion of ER-positive tumors decreased from 66.7% to 57.1% (k=0.569, p<0.001), and PR-positive tumors from 59.5% to 40.5% (k=0.377, p=0.0014) in relapse. HER2 status did not change significantly: the proportion of HER2-positive tumors was 26.2% versus 28.6% (k=0.152, p=0.203). The proportion of tumors with high Ki-67 levels increased: 66.7% compared to 69.0% (k=0.401, p=0.0006). A significant change in molecular subtype (based on ER/PR/HER2) was observed in 23.8% of patients (10 of 42), with the most common transformation being progression from the luminal B (HER2-) subtype to triple-negative cancer. Conclusion: The study demonstrates that receptor status (ER, PR, HER2) and proliferation level (Ki-67) often change as breast cancer progresses. This biological evolution of the tumor is critical for therapy selection. The results support the need for mandatory biopsy and repeat immunohistochemical testing of recurrent and metastatic lesions. This helps clarify the tumor's biological characteristics and determine the most effective, personalized treatment.