First, I'm sorry for your loss.
From what I understand they are common with the breed. Angel my oldest female has had three tumors on her right back foot. I had one of them removed and the other two are still there. They are not cancerous and aren't growing (thank God) so I've decided to leave them alone.
Honey, my youngest has one on her neck. Again, not cancerous and not growing so it hasn't presented a problem.
These tumors or bumps are often called, "Bully bumps." From the name, I'd say they are fairly common in the breed.
Of course I'm not an expert and I can't seem to find any of the web sites I had bookmarked about common health problems with the breed. If anyone else has any links I would apperciate it if you posted them.