Table 1:

Major Assays for Metastasis

Select in vitro models
Model	Description	Advantages	Limitations	Reference
Invasion/Migration Assays	Uses chambers with a wide range of chemical and properties to assess motility of cancers cell lines across physical distances	Low costs for high cell throughputs; allows for comparisons between cancer cells for their metastatic potential under a variety of conditions	Cells grow in 2D; cell migration in a petri dish may not reflect how metastasis occurs in living systems	Katt et al.(32)
Tumorspheres	Growing cancer cell lines in suspension or low binding plates to allow outgrowth in three dimensions	Since cells grow in 3D, this model more accurately represents how both mechanical and chemical factors can affect tumor formation; effective for screening anti-metastasis drugs	Many cell lines may not form tumorsphere structures, limiting this model’s use to only small subsets of cancer populations	Lee et al. (33)
Organoids	Three-dimensional cell culture technique: organoids are grown from embryonic or stem cells and resemble many of the phenotypes found in tissue of origin	intercellular communication networks and biological signaling are similar to that of original organ, allowing for more accurate drug screen assays	Random and uncontrolled growth of organoid cancer cells is common; does not accurately reflect cell communication from cells outside the original organ	Drost et al.(34); Hynds et al. (35); Kim et al. (36); Klein et al.(37)
Select in vitro models
Model	Description	Advantages	Limitations	Reference
Syngeneic Model	Engraft cancer cells that derive from the same species as the host animal	Animal retains fully competent immune system; effective for testing new immunotherapies	Does not always reflect human immune system dynamics, since animal immune system is fundamentally different	Saito et al. (38)
Humanized Mouse Model	Engraft human immune system issue into immune-deficient mice	Fast experimental kinetics; reflects human-like immune environment in animals	Humanized mice have high mortality rates than wild type mice. Grafting efficiency can also be variable from mouse to mouse.	Yin et al.(39)
Genetically Engineered Mouse Model	Knockdown/upregulation of select genes in a model mouse	Allows for isolation and subsequent study of specific genes/oncogenic pathways	Expensive; Genetically engineered mouse lines also take a long time to establish.	Walrath et al.(40)
Xenografts	Engraft human tumor tissue into humanized or immunodeficient mice	Reflects the tumor microenvironment of the original cancer sample accurately.	Many tumor types will not successfully engraft or metastasize after implantation	Saito et al. (38)