Similarly, a previous study has indicated that BMAL1 depletion increases apoptotic cell population in malignant pleural mesothelioma.22 However, previous studies by Xue et al and Hoffman et al have suggested that NPAS2 silencing does not influence the apoptotic rate in colorectal and breast cancer cells.12, 21 Possible explanations for these differences include different tumor origins and various apoptotic mechanisms. This evidence concerns the gene NPAS2 and breast cancer.