BAG3 and cancer: On the one hand, BAG3 seems to stimulate the development, invasion and metastasis of cancers by sustaining cell survival and resistance to chemotherapy; on the other hand, under proteasomal impairment or overload (e.g., under acute stress, during aging, or disorders) it mediates the disposal of degradation-prone proteins and/or aggregates by triggering selective macroautophagy.