Immunohistochemically Characterized Intratumoral Heterogeneity Is a Prognostic Marker in Human Glioblastoma

Abstract

Tumor heterogeneity is considered to be a hallmark of glioblastoma (GBM). Only more recently, it has become apparent that GBM is not only heterogeneous between patients (intertumoral heterogeneity) but more importantly, also within individual patients (intratumoral heterogeneity). In this study, we focused on assessing intratumoral heterogeneity. For this purpose, the heterogeneity of 38 treatment-naïve GBM was characterized by immunohistochemistry. Perceptible areas were rated for ALDH1A3, EGFR, GFAP, Iba1, Olig2, p53, and Mib1. By clustering methods, two distinct groups similar to subtypes described in literature were detected. The classical subtype featured a strong EGFR and Olig2 positivity, whereas the mesenchymal subtype displayed a strong ALDH1A3 expression and a high fraction of Iba1-positive microglia. 18 tumors exhibited both subtypes and were classified as “subtype-heterogeneous”, whereas the areas of the other tumors were all assigned to the same cluster and named “subtype-dominant”. Results of epigenomic analyses corroborated these findings. Strikingly, the subtype-heterogeneous tumors showed a clearly shorter overall survival compared to subtype-dominant tumors. Furthermore, 21 corresponding pairs of primary and recurrent GBM were compared, showing a dominance of the mesenchymal subtype in the recurrent tumors. Our study confirms the prognostic impact of intratumoral heterogeneity in GBM, and more importantly, makes this hallmark assessable by routine diagnostics.

Tumor Heterogeneity in Glioblastomas: From Light Microscopy to Molecular Pathology

“…A subset of GBMs contained areas of both profiles ("subtype heterogeneous") and had worse OS. Their results also confirmed the inflammatory profile of the mesenchymal subtype, which predominates in recurrent GBMs [29]. With the growing need for molecular tests to establish the final diagnosis of CNS tumors [11,21], the use of an IHC panel makes the subclassification of GBMs more speedy and affordable for oncology services worldwide.…”

“…Because of the possibility of establishing GBM prognosis by other methods, despite its importance, the transcriptomic classification of GBMs has been used more in the research field than in the clinical setting. Recently, many authors have tried to develop and validate GBM sub-classifications using histopathological features and immunohistochemistry (IHC) approaches [ 27 , 28 , 29 ]. Initially, only moderate correlation of molecular features with the histopathological grades was observed [ 15 ].…”

“…Moreover, a strong correlation between the GBM transcriptional subtypes and IHC profile was demonstrated, with higher expression of ASCL1, OLIG2, and PDGFRα in proneural GBMs; EGFR in classical GBM; and p53, pNDRG1, YKL40, and MET in mesenchymal GBM, which were able to predict the molecular subtypes with high efficacy using machine learning tools [ 27 ]. Other authors characterized a classical/proliferating profile (overexpression of EGFR and Olig2, and high proliferative activity), and a mesenchymal/microglial profile (overexpression of ALDH1A3 in tumor cells and Iba-1 in microglia) by IHC, which were closely related to the transcriptional profiles with similar names [ 29 ]. A subset of GBMs contained areas of both profiles (“subtype heterogeneous”) and had worse OS.…”

A Pilot Clinical Study of CUSP9v3: Nine Repurposed Drugs Combined With Temozolomide for the Treatment of Recurrent Glioblastoma

“…In the common aggressive cancers, and especially in GBM, phenotypic spatial and temporal heterogeneity, in both stem and non-stem subsets, is a dynamic process responding to treatment interventions and driven further and faster by hypoxia [30,[36][37][38][39]. GBM may be considered a collection of mutually interacting, mutually supporting cellular subpopulations demanding the use of a multi-drug combination to achieve prolonged treatment response.…”

Adjusting the Clock: the Importance of Circadian Rhythms in the Development of Glioblastomas and Its Intervention as a Therapeutic Strategy

“…Intratumoral heterogeneity, defined as the presence of multiple different cell subpopulations within a single tumor from one patient [13], is believed to contribute to the resistance and recurrence rate observed in GBM. Several mechanisms that cooperate to this heterogeneity have been proposed, such as the presence of cancer stem cells (CSCs) in the tumor with varying degrees of stemness and their ability to self-renew and differentiate into different types of tumor cells; heterogeneity further potentiated due to the genetic instability of the cells that leads to the generation of different subclones inside the tumor, selected by their resistance to treatment [14,15]. Besides these hypotheses, several factors could influence tumor heterogeneity, including the presence of epigenetic alterations and interactions among tumor cells and between them with the tumor microenvironment [15].…”