Table 1. In vivo models for metastasis research.

Model	Characteristics	Advantages	Disadvantages
Syngeneic model	Ingraft cancer cells that derive from the same species as the host animal	Retains a fully competent immune system; effective for testing new immunotherapies	Does not always reflect the effect of the human immune system
Humanized mouse model	Ingraft human immune system tissue into immunodeficient mice	Reflects a human-like immune environment in animals	Higher mortality rates than wild-type mice Grafting efficiency can vary
Genetically engineered mouse mode	Knockdown/upregulation of selected genes in a mouse model	Allows for the isolation and subsequent study of specific genes/oncogenic pathways	Takes a long time to render
Xenograft	Ingraft human tumor tissue into humanized or immunodeficient mice	Reflects the tumor microenvironment of the original cancer sample	Many tumor types will not successfully survive or metastasize after implantation