This pre-sensitization phenomenon might be ascribed to the ‘priming effect’ by BH3 mimetics on tumor cells (9, 45) indicating that pre-treatment could not only increase the sensitivity of tumor cells to BH3 mimetics through up-regulation of target Bcl-2 and Mcl-1 expression, but also increase of susceptibility to apoptosis via up-regulation of expression of pro-apoptotic protein BAK. The gene discussed is BCL2; the disease is neoplasm.