In breast cancer, hormone receptor (HR) status is generally a qualitative measure; either positive or negative. Quantitative measurement of HRs has often been proposed as a prognostic and predictive marker in breast cancer, some guidelines even provide different treatment options for patients with strong versus weak expression. We aimed to evaluate quantitative HR load assessed by immunohistochemistry (IHC) as a prognostic and predictive marker for patients with stage 1-3 breast cancer.
We reviewed all available literature on quantitative measurement of HRs by IHC, which is the international gold standard assay.
Combined, all included studies (n = 21) comprised a cohort of 31,146 patients. Overall, only 3 out of 19 studies found a clearly significant correlation between higher ER load and better disease outcome. Only 1 randomised trial examined quantitative ER as a prognostic marker and found no significant correlation between higher ER % and better overall survival. 4 studies addressed the predictive value of quantitative ER for response to endocrine therapy (ET) and they support no correlation between higher ER load and better response to ET. 10 studies examined quantitative PR load and only 2 of those found a significant correlation between higher PR load and better outcome. 2 randomised trials examined quantitative PR as a prognostic marker and both found no correlation between higher PR % and disease outcome. 2 studies addressed quantitative PR load as a predictive marker for response to ET, no clear correlation was found between higher PR load and better response to ET.
There is no clear evidence for using quantitative ER and PR load assessed by IHC as a prognostic measure nor as a predictive marker for response to ET in patients with stage 1-3 breast cancer. Also, as there is no clear definition of weak and strong HR expression, and given the lack of evidence for prognostic and predictive value of quantitative ER and PR load as shown in this review, “stronger” HR expression should not be used to tailor treatment decisions for women with HR positive stage 1-3 breast cancer. We recommend only using a qualitative status for hormone receptor expression in future guidelines and treatment considerations.
J.R. Kroep.
Has not received any funding.
All authors have declared no conflicts of interest.