The observations made in the limited number of clinical tumors need to be extended to a larger number of samples; nevertheless, the observation is consistent with previous evidence [35] for epigenetic silencing of RARα2 expression in MCF-7 cells and, together with the preceding observation that RARα1 rescued basal cell cycling in the ER knockdown cells, indicates that RARα1 is the relevant receptor isoform in the current study of breast tumor cells. This evidence concerns the gene ESR1 and breast neoplasm.