my 7 year old GSD had a lump on the underside of his tail. it is about the size of a conker, I noticed it some time ago while grooming him, at first I thought it was a kink, which they sometimes get, but now it seems to be getting larger, doesnt cause him any worry at all, in fact it doesnt show at all, any ideas what this could be?

Hi Charm, no idea really what it could be, think you should take him to the vet.
Christine, Spain.

our dog developed a lump under his tail when he was about 10ish. the vet said that because he had not been castrated his hormones were causing this lump next to his backside. Said it needed removing because if dog scratched or chewed it would bleed alot and chances were it would get bigger. We did not want an operations - but as the vet said it did begin to bleed and it went all over walls and carpets etc and grew. In end had to have it removed. Vet did not say whether it was cancerous or not, but once removed it did not grow back. Vet wanted to castrate dog at same time of op in case it reoccured because of hormones, but because of his age we decided not to put him through that op as well as removal of lump.

Karen.

Could be a cyst or a tumour. It should be checked out by a vet - leaving it to get too large could cause problems on a tail for finding enough skin to stretch over the wound to close it if it has to be removed.

Charm
This is a periphial ademoma they grow when a dog has not been castrated, as the dog has too much tetosterone in his body. My lad had this, the only way is get it removed and have him castrated. My lad had this done at 10 , and he came round from the op ok, and I still dont think he knows they have gone.!!!
I know you probably dont want to think of him having the op, but it may save him from getting testicular cancer, or an enlarged prostate , VERY painful, for him. My dogs burst and it was very sore and painful.

You can't know that for sure! It could be any number of possibilities. This lump probably needs to be biopsied for a definate diagnosis.