Dear friend,
I am sorry your boy has this trouble.
It sounds like a Lipoma or papilloma which is similar to a human wart and cause by a virus.
They are usually benign but any growth should be evaluated by a vet just to err on the side of caution.
http://www.peteducation.com/article.cfm?c=2+1592&aid=455
You can read more about lumps here
http://www.thepetcenter.com/exa/lumps.html
and some of the many reasons for them are listed here
http://www.peteducation.com/article.cfm?c=2+1593&aid=424
Please let me know how your boy is doing. I hope he will be just fine.
Warmest best wishes,
Terri
Healthcare Expert
Expert in canine health and behavior. 20 years of experience with dogs