"Pescecane" is indeed a colloquial term but it is not an exact synonym of "squalo", in fact the term "pescecane" is applied only to the shark species that are perceived as "typical sharks" in terms of both shape and predatory behaviour.
For example, in Italian you would not use "pescecane" to refer to a whale shark ("squalo balena") or a sawshark ("squalo sega" or "pesce sega") or a hammerhead shark ("squalo martello" or "pesce martello") and I doubt it would be used for a basking shark ("squalo elefante") but you can use it for most of the species who actively hunt and usually swim in mid-water, like a white shark (squalo bianco) or a thresher (squalo volpe) or a bull shark ("squalo leuca" or "squalo zambesi").
In other words, all "pescicani" are "squali" but not all "squali" are "pescicani" and the definition of "pescecane" is not rooted in biology or genetic but it merely depends on the stereotypical image of sharks we have in our mind.
As a final note, in biology sometimes we use "squali" (but never "pescicani") to refer to the wider group the cartilaginous fishes including also rays ("razze")