To validate and extend the preceding bioinformatics data, we initially analysed the expression of the ID2 and ID3 proteins in a series of 14 CLL (Additional file 7: Table S5) for which in vitro toxicity data was obtained for three different drugs: fludarabine, chlorambucil and ethacrynic acid. The gene discussed is ID2; the disease is B-cell chronic lymphocytic leukemia.