Figure 2. MCF7-Y537S cells are resistant to the inhibitory effects of Tamoxifen on mammosphere formation: Quantitation. Mammosphere formation assays were carried out for 5 days, in 6 well-plates, under low-attachment conditions. All the transfected MCF7 cell lines were grown as mammospheres. Note that 72h of pre-treatment with 4-OHT (1 µM) inhibits mammosphere formation efficiency (MFE), in all transfected cell lines, with the exception of MCF7-Y537S and MCF7-ESRI (WT) cells. In contrast, no changes in mammosphere formation were observed in the absence of 4-OHT (1 µM) pre-treatment. ** p< 0.005; ns = not significant evaluated by Student’s t test. (Panel A) Treated (RED) vs. Untreated (BLUE); (Panel B) Untreated; (Panel C) Treated with 4-OHT. EV, empty vector control; +, plus Tamoxilen; -, no Tamoxilen.