Active autophagy in the tumor microenvironment: A novel mechanism for cancer metastasis

Autophagy is a lysosomal degradation process which is key for the regulation of the turnover of long-lived or damaged proteins and organelles and which promotes cell survival during nutrient deprivation or other microenvironmental stresses. Current evidence supports the hypothesis that autophagy suppresses tumorigenesis, particularly during the early stages of tumor initiation. However, in established tumors, autophagy promotes survival under stressful conditions during cancer progression and in response to chemotherapy; however, the mechanism by which autophagy influences cancer metastasis remains unknown. In this review, we discuss the capacity of an abnormal tumor environment to induce autophagy and consider how this relates to tumor metastasis and the attractive prospect of manipulating autophagic signaling pathways as potential targets for the treatment of cancer metastasis.