Pistol caliber carbines are complicated in MA for two reasons (that I know of; there could be more). One: FFLs can't transfer any handgun that isn't on the approved roster and PCCs aren't on it (this can be worked around). Two: the assault weapon ban restricts standard PCC features that can't really be "fixed" by gunsmithing (e.g. 50oz weight limit; shrouded barrel; magazine attaches outside the pistol grip).

But! Rifles are controlled differently and you can get most of the popular PCCs as rifles. The problem is that the barrel must be at least 16" long, which sucks because PCCs are supposed to be short and light. You can ask the ATF to let you shorten the barrel by converting it into a short barreled rifle (an SBR), but that takes time, costs a $200 fee plus the gunsmith work, and carries with it certain restrictions that don't apply to normal rifles.