Higher ER load is not associated with better outcome in stage 1–3 breast cancer: a descriptive overview of quantitative HR analysis in operable breast cancer

PURPOSE: In breast cancer, hormone receptor (HR) status is generally a qualitative measure; positive or negative. Quantitatively measured oestrogen and progesterone receptors (ER and PR) are frequently proposed prognostic and predictive markers, some guidelines even provide different treatment options for patients with strong versus weak expression. AIM: To evaluate quantitative HR load assessed by immunohistochemistry as a prognostic and predictive measure in stage 1–3 breast cancer. METHODS: We reviewed all the available literature on quantitatively measured HRs using immunohistochemistry. RESULTS: All included studies (n = 19) comprised a cohort of 30,754 patients. Only 2 out of 17 studies found a clear correlation between higher quantitative ER and better disease outcome. Only one trial examined quantitative ER both as prognostic and predictive marker and found no association between ER% and survival. Ten studies examined quantitative PR load, only two of those found a significant correlation between higher PR load and better disease outcome. Two trials examined quantitative PR both as prognostic and predictive marker, neither found any association between PR% and disease outcome. CONCLUSIONS: There is no clear evidence for using quantitatively assessed ER and PR as prognostic nor predictive marker in patients with stage 1–3 breast cancer. We recommend only using a qualitative HR status in future guidelines and treatment considerations. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1007/s10549-019-05233-9) contains supplementary material, which is available to authorized users.