CHEK2 and breast cancer: We identified two mutations in oncogenes for each cell line: E501K of B-Raf proto-oncogene serine/threonine kinase (BRAF) and S303X of checkpoint kinase 2 (CHEK2) for BCBL-1 cells, and R108K of epidermal growth factor receptor (EGFR) and Q217X of RB transcriptional corepressor 1 (RB1) for BC-3 cells (Table 1).