one of my endler's is like that...except it's on the spine, just above the tail...I just dismissed it as a cyst of some kind, my fish aren't affected at all...
with that, I would QT Immediatly. find the cause of the problem, after that if it's treatable treat it. if not....Well.....there's a topic around here on that.
I have a few neon tetras with bumps too. One of them has had them for awhile. The bump seemed to come and go. Recently I added 10 small neons and now, a week later, about have of them have a bumpy looking torso area. They are not losing any color and seem to still be schooling.
I have an image of 2 of my neons, one with a large bump (right side of pic) and another with smaller bumps.
I am assuming I should be QT them, but for how long?