Although the number of breast tumor samples analyzed may be low, the correlation between CLOCK and ERα was statistically significant and should not be overlooked as a chance event, as subsequent experiments employing two ERα-positive breast carcinoma cell lines, MCF-7 and T47D, revealed that the levels of CLOCK protein and mRNA were indeed regulated by ERα (Fig. 2B). This evidence concerns the gene ESR1 and breast neoplasm.