STAT3 and cancer: While STAT3 knockdown alone had no significant effect on the expression levels of apoptosis markers cleaved poly (ADP ribose) polymerase (c-PARP), the latter were markedly upregulated in the BEZ235-treated STAT3 knockdown cells (Fig. 3A), indicating that STAT3 activation possibly limits the inhibitory effects of BEZ235 on cancer cell proliferation.