Table 1.

Different types of spherical cancer models in cancer biology research.

Spherical cancer model	Origin	Culture conditions
Tumorspheres Other names: • Tumor spheres • Neurospheres	Proliferations of single-cell suspension of tissue-derived cancer cells, circulating cancer cells or stablished cell lines (clonal expansion) (Singh et al., 2003) No non-neoplastic cells are present *First described for gliomas by Singh et al. (2003)	Serum-free medium (no FBS) FGF-2 and EGF are required (stem cell medium) (Lee et al., 2006; Claes et al., 2008) Grown in low-attachment conditions (i.e., no laminin-coated plates in case of glioma CSCs) Low seeding density to avoid aggregation and to foster clonal expansion
Multicellular tumor spheroids (MCTS) Other names: • Tumor spheroids	Aggregation and compaction of single-cell suspension from well-stablished cancer cell lines Rarely from single-cell suspension of tissue-derived cancer cells Heterotypic MCTS including CSCs and noncancerous cells have been reported (co-cultures) *First escribed for gliomas by Mashiyama et al. (1989)	Serum-supplemented medium (FBS or FCS) No additional growth factors Grown in non-adherent conditions promoting aggregation of cells Two culture methods: liquid overlay (LOC) and spinner cultures (SPC) (Watanabe et al., 1999). Usually by several weeks The use of U87 cells was described by Bell et al. MCTS size ranges from 400 um to 1000 um after aggregation and compaction (Bauman et al., 1999; Bell et al., 1999, 2001)
Organotypic multicellular spheroids (OMS) Other names: • Organotypic spheroids	Rounding of non-dissociated ex vivo fragments directly from surgical specimens (0.3–0.5 mm for glioma tissues) (De Witt Hamer et al., 2008) Maintain stromal components (macrophages and tumor vessels)	Cultured with liquid overlay method until they round up (2 to 5 days) Tumor microenvironment has been shown to be present up to 70 days of culture Improved genomic stability when compared to well-stablished and primary glioma cell lines Cryopreservation of glioma OMS is well-tolerated
Tissue-derived tumor spheres	Remodeling and compaction of partially dissociated (mechanically or enzymatically) tumor tissue No non-neoplastic cells reported inside the sphere	FBS-supplemented or stem cell medium

FBS, fetal bovine serum; FCS, fetal calf serum; FGF, fibroblast growth factor; EGF, epidermal growth factor; CSC, cancer stem cell; ECM, extracellular matrix; MCTS, multicellular tumor spheroid; OMS, organotypic multicellular spheroids. Based on the classification of Weiswald et al. (2015).