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Background. The primary aim of this retrospective study was to investigate intraindividual correlation of estrogen receptor (ER) status, progesterone receptor (PR) status, and HER2 status between primary breast cancer and metastatic breast cancer (mBC). Secondary aims included patients' characteristics, overall survival, feasibility of histopathological evaluation in the metastatic setting, and predictive factors associated with receptors status discordance. Methods. Patients with either biopsy of metastatic relapse or surgery of metastasis were identified. Demographics, tumor characteristics, treatment characteristics, and ER, PR, and HER2 statuses were retrospectively obtained in patients' reports. Receptors statuses were assessed by immunohistochemistry with a positivity cutoff of more than 10% for ER and PR. HER2 was considered as positive if overexpression was scored at 3ϩ in immunohistochemistry or if amplification ratio was Ͼ2 in fluorescent in situ hybridization. Results. From a cohort of 489 patients with mBC, 269 patients had histopathological samples of metastatic relapse. Histopathological analysis of the specimen confirmed the diagnosis of mBC in 235 patients. Discordance in one or more receptors between primary breast cancer and mBC was found in 99 patients (42%). A switch in receptor status was identified for ER in 17% of tumors (p ϭ 4 ϫ 10), and HER2 in 4% of lesions (p ϭ .16). Exposure to chemotherapy and to anthracycline-based chemotherapy was statistically associated with switches in ER status. Seven (2%) second malignancies and three benign diseases (1%) were diagnosed. Conclusions. This study confirms that discordance in ER and PR receptor expression between the primary breast tumor and the corresponding metastatic lesions is high, whereas HER2 status remains relatively constant. Chemotherapy, and specifically anthracycline-based chemotherapy, was associated with switch in ER status. These results were obtained in a selected population of patients; further studies are warranted to confirm these data and to determine the interest of systematic rebiopsy in the metastatic setting. TheOncologist2013;18: 667-674 Implications for Practice: Discordance in estrogen receptor and progesterone receptor expression between the primary breast tumor and the corresponding metastatic lesion was high (17% and 29%, respectively), whereas HER2 status remained stable (4% of discordance). Previous chemotherapy, and specifically anthracycline-based chemotherapy, was associated with a switch in estrogen receptor status. Further studies are warranted to confirm these data and to determine the interest of systematic rebiopsy in the metastatic setting. In the era of a more personalized approach to medicine and of genomic investigations of tumors, reliable and recent evaluation of tumor prognostic and predictive factors remains a challenge. INTRODUCTIONThe treatment of metastatic breast cancer (mBC) is complex with few recognized therapeutic standards, particularly after the first line of treatment. Multiple fa...

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