BCL2L1 and cancer: However, in order to employ Mcl-1 and Bcl-xL as diagnostic markers to predict anti-mitotic drug response in patients with distinct cancer types and heterogeneous tumor mass, we need to establish the quantitative, beyond qualitative, dependence of anti-mitotic drug response on Mcl-1 and Bcl-xL expression levels and their depletion kinetics, as well as determine to what extent the variation in the above dynamic parameters impacts the degree of variability in drug response both between cancer cell types (i.e., inter-cell line variability) and within a cancer type (intra-cell line variability).