Table 2.

Comparison of several types of patient-derived xenograft models

PDX model	Advantage	Challenges
Subcutaneous model	• Easy procedure • Minimized tissue damage of mice • Easy evaluation of tumor growth • Maintaining tumor architecture and clonality	• Lack of proper tumor microenvironment • Lack of metastasis
Orthotopic model	• Preservation of microenvironment of primary tumor • Spontaneous metastasis	• Requirement of microsurgical skills • Imaging equipment required for longitudinal study
Subrenal model	• Increased blood supply for tumor growth	• Requirement of microsurgical skills • Imaging equipment required for longitudinal study
Humanized model	• Reconstitution of human immune cells • Evaluation of cancer immunotherapy	• Requirement of long time for humanization and PDX generation • Limited reconstitution of human immune system
Stromal cell co-implantation model	• Supply of human stromal cells in tumor microenvironment	• Change of tumor characteristics by stomal cells
Circulating tumor cell (CTC)-derived model	• Minimally invasive in patient • Easy to obtain samples • Applicable for otherwise unavailable tumor specimens • Preservation of intra-tumoral heterogeneity	• Requirement of technique for the enrichment of CTCs • Variable concentration of CTCs in blood