ERBB2 and breast cancer: Although the MYBL2 gene encoding the B-Myb protein is altered in only 4% of breast cancers, increased levels of expression of this gene occur more frequently, particularly in basal-like and triple-negative (ER-, PR-, HER2-) breast cancers that generally have a poor prognosis (Amatschek et al., 2004; Thorner et al., 2009).