What Causes Growing Swelling Of A Spot On Shoulder?

MY wife s shoulder swell up and seem to get bigger has months go by. It s on top of her shoulder just above the collar bone. It started as a bruise, as though she bumped into something. A weeks go by, it swell up into a circular shape and it got bigger as months go by; about three month now, and it grew from the size of little pinky to a quarter size. It is soft when touch and does not hurt. Thanks