Circulating tumor cells and their advances to promote cancer metastasis and relapse, with focus on glioblastoma multiforme.

In the late stages of their development, cancers can form metastases. Formation of metastases was found to be associated with the capacity of cancer cells to quit the tumor mass and journey through the circulation to distant organs. This cell population is called circulating tumor cells (CTCs). They exhibit several advanced properties such as epithelial-to-mesenchymal transition (EMT) and dormancy that are essential for supporting their survival in the bloodstream, radio- and chemoresistance, their escape from the anti-cancer immune response, and metastasis initiation. CTCs, and especially dormant tumor cells, are responsible for post-surgery tumor recurrence. CTCs were detected in the blood of patients affected with glioblastoma multiforme (GBM)-the most frequent, invasive, and deadly neoplasm among primary brain tumors. The identification of glioblastoma CTCs might have a promising clinical potential for early tumor diagnosis and prognosis. A variety of CTC enrichment and detection techniques have been developed to date. For several epithelial cancers, especially for breast carcinoma, a prognostic value of CTCs was reported. Similar efforts should be performed for GBM to evaluate clinical the significance of CTCs.