I am kind of remembering or it could be wishful thinking but I remember my husband coming home with mozzie the day of his shots four weeks ago and he saying oh the vet tech said he'll have a small lump that will go away over time, I am hoping it's just due to being the bulbus from his rabies shot. You're right Poppy it doesn't always mean cancer my 13 year old female dog has a big lump on her back near her tail and she has had it for years, vet tested and said there was nothing to indicate cancer, however I need to get her back in and get her checked as it got a little bigger.