Hormone receptor and human epidermal growth factor receptor 2 (HER2) protein tests in metastatic breast cancer tissue are recommended in the guidelines of the American Society of Clinical Oncology/American Pathology Association. As part of a multi-institutional study by the National Hospital Organization, we conducted an investigation to examine these molecular markers, using cytological specimens as a substitute for tissue specimens from breast cancer metastasis. To confirm the usefulness of receptors tested in metastatic lesions, the treatment course of registered metastatic breast cancer patients was analyzed. During the April 2015 to March 2016 registration period, there were 62 registrations. Types of metastatic lesions include pleural fluid (44 samples), ascites (14 samples), lymph nodes (2 samples), pericardial fluid (1 sample), and dorsal subcutaneous mass (1 sample). A stable test result was obtained by adopting the receptor examination method, using cell block for immunostaining cytological specimens. The discordance rates of estrogen receptor (ER), progesterone receptor (PR), and HER2 protein expression were 18.2% (95% confidence interval (CI): 7.9-28.8%), 36.4% (95% CI: 23.7-49.1%), and 8.2% (95% CI: 0.1-16.3%), respectively, between the primary tumor and metastatic lesion. Patients who changed from primary negative to metastatic positive ER status had taken a significantly longer time for metastatic foci to appear. Patients with positive ER status in metastatic lesions had significantly better prognosis than ER-negative cases (P = 0.030) by the Log-Rank test. The ER status of the metastatic lesion and the metastatic site were independent prognostic factors by Cox multivariate analysis. Receptor examination with cytological specimens in metastatic lesions has been useful as it provides guidance for the treatment of metastatic breast cancer.
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