ChoKα1 and ChoKα2 are almost identical, except for a stretch of 18 extra amino acids in ChoKα1, as they result from differential splicing from the same gene, CHKA. While the implication of ChoKα1 in the regulation of cell growth and cancer has been extensively demonstrated [13], [15], [27], [28], [37], [38], [44], preliminary evidence suggest that ChoKβ may not be involved in carcinogenesis since it is not overexpressed in breast cancer cell lines [21] nor in the TRAMP mouse prostate cancer model [31]. This evidence concerns the gene CHKA and breast cancer.