Supplementary Material for: Receptor Expression Discrepancy between Primary and Metastatic Breast Cancer Lesions

<b><i>Summary</i></b><b><i>Background: </i></b>Recent studies have shown that the expression status of hormone receptors and human epidermal growth factor receptor 2 (HER2) in breast cancer may change during disease progression. The aim of this study was to determine and compare the estrogen receptor (ER), progesterone receptor (PR), and HER2 expression status in primary breast cancer and metastatic lesions. <b><i>Methods: </i></b>58 patients with registered biopsy reports or available samples of the primary tumor and distant metastases were included in the final analysis. Biopsy samples were re-stained using immunohistochemical methods to determine receptor status (if not already recorded in previous reports) and re-examined by 2 independent pathologists. <b><i>Results: </i></b>Discordance rates for receptor expression status of the primary tumor and distant metastases for ER, PR, and HER2 were 17.4, 45.4, and 13.3%, respectively. No statistically significant difference in overall survival due to receptor expression discordance between the primary tumor and metastatic sites (p &gt; 0.05) was found, although a tendency toward worse survival time was observed in patients with HER2 expression discrepancies. <b><i>Conclusion: </i></b>This study showed receptor discordance rates between primary and metastatic breast cancer sites for ER, PR, and HER2 of 17.8, 45.4, and 13.3%, respectively. Re-biopsy and IHC evaluation of metastatic sites for receptor status may change treatment decisions in patients with relapsed/progressed BC.