ERBB2 and breast cancer: Based on the notion that chemotherapy treatment increases the percentage of CD44high/CD24low cells [75], Li and colleagues demonstrated that while the treatment of a “mixed” BC patient cohort with chemotherapy increased the percentage of CD44high/CD24low cells and induced the formation of mammospheres, the combinatorial administration of chemotherapy plus lapatinib in specific HER2+ BC cases did not lead to the accumulation of CD44high/CD24low BCSCs, indicating that the mesenchymal BCSC compartment is not totally refractory to lapatinib activity [75].