They are not cancers and do not metastasize. Remember that excision gets rid of the cholesteatoma, but not the eustachian tube dysfunction and sometimes these recur. A PE tube will prevent chronic negative middle ear pressure. One other way to get a cholesteatoma is for squamous epithelium to migrate into the middle ear space through a hole in the tympanic membrane. The hole can come from a previous severe necrotizing infection, a previous PE tube hole that didn't heal, or trauma.
Marginal perforations are more likely to allow migration than central ones.
When there is a perforation all three layers start to proliferate, but if the squamous layer and the cuboidal layer meet, the fibrous layer will stop. This can lead to a chronic perforation. The logic behind this older nomenclature is that the middle ear is constantly being exposed to the outside and has a low grade inflammation chronically associated with it. Curiously, a perforation usually does not give you much of a hearing loss. He is otherwise healthy.