A methodological comparison between protein expression measurement of ER, PR, and HER2 by IHC versus their respective mRNA levels by RT-qPCR showed that detection of mRNA levels by RT-qPCR is a better approach for subtyping breast cancer and predicting the prognosis (Du et al., 2013; Wirtz et al., 2016). The gene discussed is PGR; the disease is breast cancer.