An invadopodia is a structure observed on the surface of certain cells, notably epithelial cells.
It takes the form of an invagination, with finger-shaped extensions inside of it. Each of these protuberances consists of an actin core surrounded by a certain number of proteins, forming a ring. Due to their shape, these structures used to be called rosettes.
They seem to be associated with the invasive processes of tumour cells, and more precisely, involved in the destruction of extracellular matrices, the basal membranes. This is why they are called invadopodia.
Other structures, which are only different in terms of architectural details, have been observed on other types of cells, and are called podosomes. The difference between these two types of structures is still vague.