Clinical Stratification of Glioblastoma Based on Alterations in Retinoblastoma Tumor Suppressor Protein (RB1) and Association With the Proneural Subtype

Abstract

A recent study of CDK4/6-inhibitors in glioblastoma (GBM) xenografts identified retinoblastoma tumor suppressor protein RB1 status as a determinant of tumor therapeutic efficacy. Because of the need for clinically applicable RB1 testing, we assessed the utility of 2 complementary methods for determining RB1 status in GBM. Using fluorescence in situ hybridization (FISH) and immunohistochemistry (IHC), we analyzed 34 GBMs that had also undergone molecular characterization as part of The Cancer Genome Atlas (TCGA). By IHC, 4 tumors (11.8%) had complete loss of RB protein expression, including 2 with homozygous deletion of RB1 by FISH and 1 with hemizygous deletion of RB1 by FISH combined with a novel nonsense mutation in RB1. Consistent with these results, in an independent set of 51 GBMs tested by IHC we demonstrated loss of RB1 protein in 5 (9.8%). In GBM molecular subtype analysis of TCGA data, complete loss of RB1 transcript expression was seen in 18 of 170 tumors (10.6%) and these were highly enriched for, but not exclusive to, the proneural subtype (p < 0.01). These data support the use of IHC for determining RB1 status in clinical GBM specimens and suggest that RB1 alterations may be more common in certain GBM subgroups.

Results of immunohistochemical staining for cell cycle regulators predict the recurrence of atypical meningiomas

“…In particular, several studies have documented the role of RB protein in the prognosis and progression of malignant brain tumors such as glioblastoma. 7,14,16 Among these works, the study by Hilton et al 16 suggested that glioblastomas showing widespread immunohistochemical expression of RB protein have a better prognosis than those without this feature, which is different from our results. However, the authors did not separate RB protein into phosphorylated and unphosphorylated forms.…”

Results of Immunohistochemical Staining of Cell-Cycle Regulators: The Prediction of Recurrence of Functioning Pituitary Adenoma

“…The cumulative number of aberrantly expressed cell-cycle and proliferative markers correlated with aggressive pathologic features and inferior oncologic outcomes in patients with renal cell carcinoma (11), gallbladder malignancies (46), gastric adenocarcinoma (25), and breast cancer (14). In addition, there are several studies reporting the role of RB protein in prognosis and progression of malignant brain tumors, such as glioblastoma (3,12,16,52,53). Among them, Hilton et al (16) suggested that glioblastoma showing widespread immunohistochemical expression of RB protein have a better prognosis than those without these features, which was opposite to our results.…”

Phase-2 trial of palbociclib in adult patients with recurrent RB1-positive glioblastoma

“…RB1 IHC was performed on archival formalin-fixed, paraffin-embedded tissue using the Ventana Medical Systems Benchmark XT and the iView detection system and quantified as previously described [10]. Slides were deparaffinized in xylene, and rehydrated through ethanol.…”