Several preclinical studies have investigated this phenomenon; Graham M. et al. validated a new flow cytometry-based immunoassay and associated software for the simultaneous quantification of PgR levels and DNA indices of ploidy and cell cycle stages in any subset of the total cell population using the human BC cell line T47D and its clonal derivatives, and demonstrated a remarkable heterogeneity in PgR expression, thus confirming the existence of distinct tumor cell subclones that show a mixed response to antiestrogen treatment with tamoxifen [82]. This evidence concerns the gene PGR and breast cancer.