ESR1 and breast carcinoma: The high yields (9/9) of ERα expressing cell clones in the TN-derived ERα-deficient breast carcinoma cell line MDA-MB-231 stands in contrast to previous studies carried out in our laboratory (and described in part above), as well as those of others (mentioned before), in which the efficiency of generating stable ectopic ERα expressing breast carcinoma cells is a cumbersome and inefficient procedure, resulting in a mere ∼5% valuable clones.