Brain malignancies: Glioblastoma and brain metastases

Semin Cancer Biol. 2020 Feb;60:262-273. doi: 10.1016/j.semcancer.2019.10.010. Epub 2019 Oct 22.

Abstract

Brain, the major organ of the central nervous system controls and processes most of body activities. Therefore, the most aggressive brain tumor - glioblastoma and metastases from other organs to the brain are lethal leaving the patients with very short time of survival. The brain tissue landscape is very different from any other tissues and the specific microenvironment, comprising stem cells niches and blood-brain barrier, significantly influences the low rate of glioblastoma metastasis out of the brain, but better accommodates brain-invading cancer. In contrast to low frequency (0.5%) of all glioblastoma metastases, 10%-45% of other primary cancers do metastasize to the brain. This review addresses general cellular and molecular pathways that are to some extent similar in both types of metastases, involving circulating tumor cells (CTCs) with cancer stem cells (CSCs) characteristics, and metastatic niches. The invasion is a dynamic process involving reversible epithelial-to-mesenchymal (EMT) cell process, creating a transient gradient state that is inter-connected with epigenetic plasticity of the metastasizing (m)CSCs. These cells can switch between stationary, low proliferating/dormant state to a migratory, mesenchymal-like state. Settling in their respective niches as dormant CSCs in the secondary organ is a common feature in all types of metastases. In glioblastoma metastasis, the malignant mGSC cells express markers of mesenchymal GSC subtype (MES-GSC), such as CD44 and YK-40 and their major obstacle seems to be propagating in the in various organs' microenvironments, different from the niches that home GSCs in the primary glioblastoma. Focusing on one stromal component in the glioblastoma niches, the mesenchymal stem cells (MSCs), we report herein on their differential effects on glioblastoma cells, highly depending on their genetic subtype. On the other hand, in brain metastases, the major hindrance to metastatic progression of mCSCs seem to be crossing the blood-brain-barrier. Novel therapeutic approaches for brain metastases from various cancer types are advancing slowly, and the general trends involve targeting metastatic sub-clones and selective determinants of their niches. The update on the four most common brain metastases from lung, breast, melanoma and colorectal carcinoma is presented.

Keywords: Brain; Cancer stem cells; Glioblastoma; Invasion; Metastasis; Microenvironment.

Publication types

  • Research Support, Non-U.S. Gov't
  • Review

MeSH terms

  • Animals
  • Biomarkers
  • Brain Neoplasms / diagnosis
  • Brain Neoplasms / secondary*
  • Brain Neoplasms / therapy
  • Disease Management
  • Disease Progression
  • Disease Susceptibility
  • Glioblastoma / diagnosis
  • Glioblastoma / etiology*
  • Glioblastoma / metabolism
  • Glioblastoma / therapy
  • Humans
  • Neoplasm Metastasis
  • Neoplastic Cells, Circulating
  • Neoplastic Stem Cells / metabolism
  • Neoplastic Stem Cells / pathology
  • Stem Cell Niche
  • Stromal Cells / metabolism
  • Stromal Cells / pathology
  • Tumor Microenvironment / genetics
  • Tumor Microenvironment / immunology

Substances

  • Biomarkers