Want to throw another thread on cell model which is, in my option, also critical to study cancer metastasis. My ideal model is **genetically engineered immunocompetent mouse model that develop primary tumor and metastasis **. Engineering known oncogenes like KRAS, MYC, or tumor suppressors like P53, p16 recapitulates human tumor and is highly reproducible. Immunocompetent is critical to study the effects of microenvironment and immune system to tumor and metastasis development. By doing single-cell RNA-Seq profiling of primary and metastatic tumor cells and their surrounding stroma cells, as well as blood(spleen), bone marrow, we should be able to build comprehensive and extremely valuable dynamic molecular maps of the real metastasis process. I do know a good model like that (PTEN/P53 null driven liver tumor and lung metastasis) from my colleague Liqin Zhu at St. Jude, but there is an extra cancer stem cell enrichment ex-vivo culture to make the metastasis development faster. It was a byproduct of her Cell paper last year: https://www.ncbi.nlm.nih.gov/pubmed/27565343. Not sure if any other model exists. Comments and suggestions are welcome! Thanks.