Abstract
PURPOSE: There is cumulative evidence that changes in biomarker status occur frequently during the metastatic progression of breast cancer and affect treatment response. The purpose of this study was to evaluate the frequency of biomarker changes in metastatic breast cancer (MBC) and its impact on prognosis. METHODS: A total of 152 patients diagnosed with MBC at the time of initial diagnosis or during post-surgical follow-up were included. Changes in biomarker status in MBCs, their frequency according to various metastatic sites, tumor characteristics, and their association with patient survival were analyzed. RESULTS: Estrogen receptor (ER), progesterone receptor (PR), human epidermal growth factor receptor 2 (HER2), and Ki-67 status changed in 9 (6.0%), 40 (26.3%), 12 (7.9%), and 29 (19.1%) patients, respectively. ER, PR, and HER2 mainly showed positive to negative conversion, whereas Ki-67 changed mostly from a low to high index. There were no differences in the frequencies of biomarker changes according to the metastatic sites. As for ER and HER2, cases with negative conversion showed low expression levels in the primary tumor. Survival analyses indicated that a positive to negative conversion of ER was an independent poor prognostic factor in patients with primary ER-positive breast cancer. CONCLUSION: Changes in biomarker status are not rare, and usually occur in an unfavorable direction in breast cancer metastases. Negative conversion of ER status is a predictor of poor prognosis. Thus, it is beneficial to evaluate changes in biomarker status in MBC not only for the purpose of determining treatment options but also for prognostication of patients.