Autophagy in pituitary tumors

Autophagy or self‐cannibalism, is degradation of cytoplasmic constituents providing an alternative energy source and allowing cell survival during hypoxia, nutrient deprivation and metabolic stress. Formation of membranes engulfing part of the cytoplasm, fusion with lysosomes and degradation can be conclusively seen by electron microscopy. To our knowledge, no information is available to date on the role of autophagy in pituitary tumors. We investigated more than 5000 surgically removed human pituitary tumors by electron microscopy. Our results indicate that autophagy is rare and can be demonstrated in every adenohypophysial tumor type. Autophagy is most frequently noted in long acting somatostatin analog treated GH producing and in dopamine agonist treated PRL producing pituitary adenomas. These two treatment modalities which cause tumor shrinkage, clinical and endocrinological improvement, activate autophagy. Many cytotoxic and anticancer drugs stimulate autophagy and counteract the effect of therapy in many tumor types resulting in tumor cell survival. New drugs are needed which inhibit autophagy. It remains to be seen whether anti‐autophagic drugs would suppress the formation of additional nutrients, eliminate the extra energy source and increase the efficiency of drugs used in the treatment of pituitary tumors. This study was supported by the Jarislowsky and Lloyd Carr‐Harris Foundations.