However, the clinical behavior of luminal-type breast cancer can be markedly heterogeneous despite similar levels of ER expression [57]; therefore, a set of genes differentially regulated in MCF-7-14 cells (PIK3R1, SOCS2, BMP7, CD44 and CD24) may be useful markers to identify among good prognosis tumors those that will relapse and metastasize. This evidence concerns the gene ESR1 and breast cancer.