tumors are thought to originate from a small population of undifferentiated cells having characteristics of normal neural stem cells. These cells have been named after brain tumor stem cells, responsible for tumor initiation and therapy resistance in primary brain tumors (6). Aldehyde dehydrogenase 1 (ALDH1) is a detoxifying enzyme that catalyzes oxidation of intracellular aldehydes, leading to production of retinoic acid from retinol, which has a major role in cell proliferation and differentiation and maintenance of stem cell phenotype. ALDH1 is needed for resistance to alkylating agent through its detoxifying effect (7, 8). This biomarker has been detected in stem cells of both normal and neoplastic tissues (9). Polycomb group (PcG) proteins have a major role in regulating several physiological and pathological activities, such as oncogenesis (10). PcG protein complexes are Prognostic Value of ALDH1, EZH2 and Ki-67 in Astrocytic Gliomas Shimaa Ahmed1, Hayam Rashed1, Abdelmonem Hegaz y2, Abdel Motaleb Mohamed3, Wael Elmesalla my4 Department of 1Pathology, 2Anatomy and Embryology, 3Clinical Oncology and Nuclear Medicine and 4Neurosurgery, Zagazig University, Faculty of Medicine, Zagazig, Egypt ABSTRACT Objective: Tumor stem cells have been found in a variety of neoplasms and stated to have a role in tumor progression. This study aimed to evaluate the prognostic significance of biomarkers which are said to be related to these cells, i.e., EZH2, ALDH1 and Ki-67, and their correlation with each other in astrocytic gliomas. Material and Method: Formalin-fixed, paraffin-embedded tissue specimens of 40 patients with astrocytic glioma who underwent initial surgery during the period from December 2011 to May 2014 at Zagazig University Hospitals were enrolled in the study. Consecutive 4-μm thick sections from formalin-fixed, paraffin-embedded tissue blocks were prepared and stained with hematoxylin and eosin for histopathological evaluation. Immunohistochemical analysis using ALDH1, EZH2 and Ki-67 antibodies were performed to examine the cases. Results: A total of forty patients; 22 males and 18 females were studied. The lesions were classified as follows: 14 cases of low-grade astrocytoma (WHO grade I or II), 11 cases of anaplastic astrocytoma (WHO grade III), and 15 glioblastomas (WHO grade IV). There was a significant increase in ALDH1 immunoreactivity with increasing the grade of astrocytoma (mean ±SD = 0.2 ±0.4, 0.5 ±0.6, 1.1 ±1.3 and 2.95 ±2.97 in grade I to IV astrocytic gliomas, respectively). This expression was significantly correlated with overall survival (OS) and progression-free survival (PFS) (P=0.004). EZH2 expression was also significantly associated with advanced grades (mean ±SD =1.35 ±0.4, 3.1 ±2.6, 7.2 ±3.5 and 9.9 ±4.1, in grade I to IV astrocytic gliomas, respectively). EZH2 and Ki-67 expressions were found to be correlated with OS and PFS (P < 0.001).