The metastatic process, i.e. the dissemination of cancer cells throughout the 
body to seed secondary tumors at distant sites, requires cancer cells to leave 
the primary tumor and to acquire migratory and invasive capabilities. In a 
process of epithelial-mesenchymal transition (EMT), besides changing their 
adhesive repertoire, cancer cells employ developmental processes to gain 
migratory and invasive properties that involve a dramatic reorganization of the 
actin cytoskeleton and the concomitant formation of membrane protrusions 
required for invasive growth. The molecular processes underlying such cellular 
changes are still only poorly understood, and the various migratory organelles, 
including lamellipodia, filopodia, invadopodia and podosomes, still require a 
better functional and molecular characterization. Notably, direct experimental 
evidence linking the formation of migratory membrane protrusions and the process 
of EMT and tumor metastasis is still lacking. In this review, we have summarized 
recent novel insights into the molecular processes and players underlying EMT on 
one side and the formation of invasive membrane protrusions on the other side.