Thus, by evaluating the expression of both CYP27A1 mRNA and protein expression in the same tumor series from premenopausal patients, this study has demonstrated that intratumoral CYP27A1 transcript and protein expression are moderately correlated and that high protein and mRNA expression of CYP27A1 are both prognostic of a favorable outcome in premenopausal patients with ER+ BC, albeit to a varying extent. The gene discussed is ESR1; the disease is breast cancer.