Many keepers have experienced various growths or abcesses, which have had varying degrees of severity or long-term impact to their chams.
You'll need to post some photos of the growth before anyone will be able to provide some meaningful advice for your cham.
Generally speaking though, external growths are never good for your cham, and they don't often go away on their own. You should probably take your cham to a vet to be checked out.