Receptor Discordance During the Treatment Course of Patients With Metastatic Breast Cancer: Results From the SONABRE Registry

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PURPOSE: The aim was to evaluate factors associated with taking 2 biopsies during the disease course of metastatic breast cancer (mBC) and to assess discordance rates for the oestrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2). METHODS: Patients diagnosed with mBC in ten Dutch hospitals between 2007 and 2020 were retrieved from the SONABRE Registry (NCT-03577197). Patients were identified if they had at least 2 biopsies at different time points during their mBC disease course. Last follow-up was collected in September 2023. Frequencies and factors related to a second biopsy were studied using competing risk analysis with subdistribution hazard ratios (sHR). Discordance rates and factors associated with receptor subtype discordance were analysed using logistic regression using odds ratios (OR). RESULTS: Of 4,470 patients with mBC, 65% had 1 and 10% 2 biopsies during the course of mBC. Having 2 biopsies for mBC was related to age (sHR: 0.61), comorbidity (sHR: 0.76), WHO performance score (sHR: 0.30 for ≥2), initial TN subtype (sHR: 0.67), and initial metastatic site (sHR: 3.68 for soft tissue only), compared with the reference categories. Patients had an overall receptor subtype discordance of 23% compared to the second biopsy. Only HR+/HER2+ status was related to receptor subtype discordance (OR: 6.45). CONCLUSION: Only the minority of patients with mBC underwent a second biopsy during their mBC disease course. Receptor subtype heterogeneity is however frequent, particularly in patients with initially HR+/HER2+ mBC. Future studies are needed to guide treatment decisions as heterogeneity may play a role.

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