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Pharmacol Ther. 2019 Feb;194:161-184. doi: 10.1016/j.pharmthera.2018.09.007. Epub 2018 Sep 28.

Hybrid epithelial/mesenchymal phenotypes promote metastasis and therapy resistance across carcinomas.

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Center for Theoretical Biological Physics, Rice University, Houston, TX, USA. Electronic address:
Duke Cancer Institute and Department of Medicine, Duke University Medical Center, Durham, USA.
Blizard Institute, Barts and the London School of Medicine and Dentistry, Queen Mary University of London, London, UK.
Department of Clinical Cancer Prevention, UT MD Anderson Cancer Center, Houston, USA.
National Center for Cell Science, Savitribai Phule Pune University Campus, Ganeshkhind, Pune, India.
Department of Molecular Reproduction, Development & Genetics, Indian Institute of Science, Bangalore, India.
Center for Theoretical Biological Physics, Rice University, Houston, TX, USA. Electronic address:


Cancer metastasis and therapy resistance are the major unsolved clinical challenges, and account for nearly all cancer-related deaths. Both metastasis and therapy resistance are fueled by epithelial plasticity, the reversible phenotypic transitions between epithelial and mesenchymal phenotypes, including epithelial-mesenchymal transition (EMT) and mesenchymal-epithelial transition (MET). EMT and MET have been largely considered as binary processes, where cells detach from the primary tumor as individual units with many, if not all, traits of a mesenchymal cell (EMT) and then convert back to being epithelial (MET). However, recent studies have demonstrated that cells can metastasize in ways alternative to traditional EMT paradigm; for example, they can detach as clusters, and/or occupy one or more stable hybrid epithelial/mesenchymal (E/M) phenotypes that can be the end point of a transition. Such hybrid E/M cells can integrate various epithelial and mesenchymal traits and markers, facilitating collective cell migration. Furthermore, these hybrid E/M cells may possess higher tumor-initiation and metastatic potential as compared to cells on either end of the EMT spectrum. Here, we review in silico, in vitro, in vivo and clinical evidence for the existence of one or more hybrid E/M phenotype(s) in multiple carcinomas, and discuss their implications in tumor-initiation, tumor relapse, therapy resistance, and metastasis. Together, these studies drive the emerging notion that cells in a hybrid E/M phenotype may occupy 'metastatic sweet spot' in multiple subtypes of carcinomas, and pathways linked to this (these) hybrid E/M state(s) may be relevant as prognostic biomarkers as well as a promising therapeutic targets.


Cancer metastasis; Cancer stem cells; Collective cell migration; Epithelial-mesenchymal transition; Hybrid epithelial/mesenchymal; Phenotypic plasticity

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