Brain Tumor Cells in Circulation Are Enriched for Mesenchymal Gene Expression

Abstract

Glioblastoma (GBM) is a highly aggressive brain cancer characterized by local invasion and angiogenic recruitment, yet metastatic dissemination is extremely rare. Here, we adapted a microfl uidic device to deplete hematopoietic cells from blood specimens of patients with GBM, uncovering evidence of circulating brain tumor cells (CTC). Staining and scoring criteria for GBM CTCs were fi rst established using orthotopic patient-derived xenografts (PDX), and then applied clinically: CTCs were identifi ed in at least one blood specimen from 13 of 33 patients (39%; 26 of 87 samples). Single GBM CTCs isolated from both patients and mouse PDX models demonstrated enrichment for mesenchymal over neural differentiation markers compared with primary GBMs. Within primary GBMs, RNA in situ hybridization identifi ed a subpopulation of highly migratory mesenchymal tumor cells, and in a rare patient with disseminated GBM, systemic lesions were exclusively mesenchymal. Thus, a mesenchymal subset of GBM cells invades the vasculature and may proliferate outside the brain. SIGNIFICANCE:GBMs are locally invasive within the brain but rarely metastasize to distant organs, exemplifying the debate over "seed" versus "soil. " We demonstrate that GBMs shed CTCs with invasive mesenchymal characteristics into the circulation. Rare metastatic GBM lesions are primarily mesenchymal and show additional mutations absent in the primary tumor.

Extraneural metastases in glioblastoma patients: two cases with YKL-40-positive glioblastomas and a meta-analysis of the literature

“…In particular, both the reported cases express YKL-40, lack of EGFR amplification, and show no MGMT promoter hypermethylation (Bath et al, 2013), orienting to a mesenchymal profile. Recently, another group confirmed such hypothesis, exploring CTC and showing as mesenchymal phenotype relates to higher risk of developing extraneural metastasis (Sullivan et al, 2014). As the authors stressed, the molecular GBM analysis could bring to a comprehensive knowledge of the tumoral process, including the early identification of GBM subtypes prone to extraneural localization.…”

The Evolving Role of Molecular Markers in the Diagnosis and Management of Diffuse Glioma

“…1). Advances in minimally invasive means to sample and detect key genomic aberrations in glioma, such as cellfree nucleic acid (84,85) or circulating tumor cells (86). As the process of therapeutic refinement moves forward, more effective preclinical models and optimal clinical trial design will be absolutely crucial, as will the ready availability of sophisticated genomic technology in the clinical environment, starting with the use of relevant molecular markers as an objective means for tumor classification.…”

Cancer, Oxidative Stress, and Metastasis

“…Circulating cancer cells are commonly observed in the blood of patients and mice with various cancers (Nagrath et al 2007;Stott et al 2010;Yu et al 2013Yu et al , 2014Sullivan et al 2014). Nevertheless, metastasis is a very inefficient process as very few metastasizing cancer cells survive and even fewer proliferate to form micrometastases (Luzzi et al 1998;Cameron et al 2000;Kienast et al 2010).…”