CD44 and breast cancer: In addition, we performed clonogenic assays as in vitro tests for self-renewal (Fiebig et al, 2004) in a panel of cell lines from Tables 1 and 2; the percentage plating efficiency representing colony-forming units in the whole cell population was highest in cell lines with a large SP, such as MCF-7/HER2-18, and lowest in those BC cells lacking an SP and HER2, expressing low levels of CD44+/CD24−, but exhibiting a high ALDH1+ fraction (MDA-MB-468) (Figure 1C).