Its scary stuff aye? DS4 gets lumps all the time.
He had the works surgery done last year tonsils, grommets, adenoids, biopsies and they also removed one lump that just wouldn't go away.
Apparently he is just one of those kids that his infections affect him there and he is currently sporting another lump at the moment from a sore throat a few Weeks ago.
Be prepared for them to come back again but at least this time you know what you are dealing with.