PGR and breast cancer: As is well known, BC tissues are divided clinically into different subtypes according to ER, PR, and ERBB2 expression levels.42,43 Although the usefulness of ER, PR, and ERBB2 for clinical classification focuses on the selection of responses to treatments, such a conventional examination could not predict prognosis with sufficient accuracy on the basis of the multivariate analyses.44,45 Estrogen receptor, PR, and ERBB2 were not identified as independent predictive factors after the multivariate Cox proportional hazards regression analysis.