Incidence and Prognostic Significance of Hormonal Receptors and HER2 Status Conversion in Recurrent Breast Cancer: A Retrospective Study in a Single Institute

<i>Background and Objectives</i>: Changes in biomarker status are not rare and usually occur in an unfavorable direction. Evaluating changes in biomarker status is advantageous for assessing treatment options and prognosticating patients. Currently, only a few studies have explored the association between biomarker conversion and breast cancer relapse. In this study, we sought to determine the incidence of receptor conversions in patients diagnosed with recurrent breast cancer in comparison to their corresponding primary tumors and to evaluate possible influencing factors. Moreover, we aimed to assess the prognostic significance of biomarker conversion, if any was detected, in breast cancer patients. <i>Materials and Methods</i>: A retrospective cohort study was conducted among breast cancer patients treated at King Khalid University Hospital, Riyadh, Saudi Arabia. Data were collected from recurrent breast cancer patients about different parameters to assess the incidence of hormonal receptors and human epidermal growth factor 2 (HER2) status conversion between primary and recurrent tumors. The calculation of progression-free survival (PFS)/ relapse-free survival (RFS) and the overall survival (OS) was conducted to assess the prognostic value of the assessed biomarker conversion. <i>Results</i>: Progesterone receptor (PR) conversion had the highest incidence (29.9%), followed by HER2 (23%) and estrogen receptor (ER) (12.6%). Menopausal status and concurrent receptor conversion were significant factors influencing receptor status changes. However, no significant associations were found between receptor conversion and other clinical factors, including tumor stage and histological subtype. The survival analysis revealed no statistically significant differences in OS or RFS between patients with and without receptor conversion. <i>Conclusions</i>: Receptor conversion, particularly for PR and HER2, is common in recurrent breast cancer, emphasizing the importance of re-biopsy at recurrence to ensure accurate treatment decisions. While receptor conversion does not significantly impact survival outcomes in this cohort, further large-scale prospective studies are warranted to validate these findings and explore their clinical implications in breast cancer management.