Characterization of Stem Cell Markers in Pheochromocytomas and Paragangliomas

Pheochromocytomas (PCC) are categorized in adrenal and extra-adrenal forms (paragangliomas). 11 germ line mutations so far could be found to be associated with PCC, and seem to play a role in approximately 33% of cases. Approximately 10% of PCC are malignant. To date, no marker to predict malignancy or metastatic disease could be found, so that identification of metastases renders the proper diagnosis in the end. Stem cell-like cancer cells, by their ability to proliferate, to give rise to a variety of different tumor cells, and to withstand chemotherapeutic regimens, were found to be responsible for most of the malignant behavior and aggressiveness in several tumor types. Whether these cells play a role in PCC is not known. We screened a PCC microarray database for different widely accepted stem cells markers and found C-KIT (1.58 fold change, p = 0.01), THY1 (1.51 fold change, p < 0.01), PREF1 (1.63 fold change, p = 0.05), and MSI2 (-2.03 fold change, p < 0.01) most differentially expressed. SOX2, LIN28, NGFR, THY1, PREF1, SOX17, NESTIN, CD117, OCT3/4, NANOG, CD133 were further examined on 208 PCCs with different genetic backgrounds by tissue array analysis. In this cohort, SOX2, LIN28, NGFR, and THY1 expression was found in more than 10% of tumors, while PREF1, SOX17, NESTIN, and CD117 were expressed less frequent, and OCT3/4, NANOG and CD133 were not detectable at all. Stem cell marker expression was associated with positive succinate dehydrogenase (SDHx) mutation status. Double-staining for Chromogranin A/SOX2 and S100/SOX2 revealed SOX2 expression both in tumor and adjacent sustentacular cells. In addition, NGFR expression was significantly correlated with malignant disease (42 vs. 16%, p = 0.04). In summary, these data indicate that a subset of PCC contain subpopulations of stem cell marker-positive cells. Further studies are required to validate whether NGFR expression could be utilized as a predictor for malignancy.