Generally, EMT, Epithelial to Mesenchymal Transition is thought to be involved in the mechanism in which cancer cells metastasize in the early stage. EMT is an process in which epithelial cells depolarize and lose their cell-to-cell contacts, and gain mesenchymal morphology. The mesenchymal cells is capable of reaching distant sites through the blood vessels. So, EMT is thought to be a necessary mechanism for metastasis.
However, I found a surprising report from Nature article indicating that EMT isn't required for metastasis:
Fischer, Kari R. et al. "EMT Is Not Required for Lung Metastasis but Contributes to Chemoresistance." Nature 527.7579 (2015): 472–476.
They established an EMT lineage-tracing system in mice with the mammary tumors to monitor metastasis of the epithelial cancer cells to lung through EMT using epithelial-specific and mesenchymal-specific markers. This report showed that a small proportion of cancer cells underwent EMT and lung metastasis mainly consisted of epithelial cells which didn't undergo EMT.
I think this report is innovative and overthrows the commonly accepted thought that EMT is necessary for metastasis, However, some questions come to me.
How the epithelial cancer cells gain the motility and metastasize without undergoing EMT？