Receptor Discordance of Metastatic Breast Cancer Depending on the Molecular Subtype.

INTRODUCTION: Almost 30% of all women with early-stage breast cancer develop metastases. Treatment of metastatic disease is often based on the immunohistochemical information of the primary tumor, despite possible discordance of the hormone and Her2 receptor status. OBJECTIVES: The aim of this study was to compare the receptor status of the primary tumor with the metastasis, and to evaluate for receptor discordance with regard to the molecular subtype, receptor status, and the localization of the metastases. METHODS: We retrospectively analyzed the data of all consecutive women with metastatic breast cancer, who underwent treatment at the Medical University Vienna between 2009 and 2016. Associations were calculated using the χ2or Fisher's exact test; years from primary diagnosis to metastatic disease were calculated using the Kaplan-Meier method. RESULTS: We identified 213 metastatic breast cancer patients, of whom 67 (31.5%) showed a discordant receptor status. Out of 32 patients with luminal A subtype, 14 (43.8%) had a switch of at least one receptor; 27 of 53 patients (50.9%) with luminal B subtype and 21 of 32 patients (65.6%) with Her2+ subtype showed receptor discordance; for triple-negative disease, 5 of 19 patients (36.3%) had a switch of at least one receptor. In 63 samples of bone metastases, 13 (20.6%) had discordant estrogen receptor status (p = 0.04). In 55 samples of bone metastases, 35 (63.3%) had discordant Her2 status (p = 0.002). CONCLUSIONS: Our data show high rates of receptor discordance in metastatic breast cancer. Apart from the primary tumor, the immunohistochemical receptor status of the metastasis needs to be verified. This can lead to a change in treatment and prognosis.