The purposes of this study were to address a persistent controversy as to whether the ER status of a primary tumor remains stable during progression to metastasis and to evaluate the influence of disease course and prior systemic therapy on ER status.
Breast carcinomas from 227 women with known ER status in both primary tumor and paired metastasis were retrospectively reviewed. ER status was compared between primary and metastatic tumors with respect to metastatic site, interval between two ER assays, and intervening chemotherapy and endocrine therapy. Semiquantitative comparison of ER values was performed for 92 tumor pairs.
ER status agreed in 210 (92.5%) patients, including 147 positive and 63 negative. Of the 17 patients (7.5%) with discordant ER status, both negative to positive conversion (n = 7) and positive to negative conversion (n = 10) were observed. ER discordance was not significantly associated with metastatic site (locoregional vs distant), time interval between assays (< 5 years vs. ≥ 5 years), or intervening chemotherapy and endocrine therapy. Semiquantitative levels of ER expression were similar between primary and metastatic tumors. In discordant cases, variations in testing methods and marginal scores were common.
ER status in breast carcinoma is generally stable during progression to metastasis. Preanalytical and analytical variability may contribute to discordance in some cases. Given the importance of ER status for clinical management, ER testing in metastatic breast carcinoma should be repeated, especially for patients whose clinical courses are not compatible with stated ER status.