SMAD4 and neoplasm: When the growth-promoting signals TGF-β and SMAD4 are sensed by PDAC cells, the survival conditions at this time are favorable for tumor cells, and autonomous autophagy assists tumor cell growth instead of invision; when SMAD4 deletion results in unfavorable survival conditions for tumor cells, TGF-β induces autonomous autophagy to activate another compensatory survival pathway, the MAPK/ERK pathway, and at the same time autonomous autophagy activates EMT to increase the invasive behaviors to avoid survival crisis.