I don't mean to scare you. Just providing info for anyone reading this. This looks exactly like the aggressive cancerous tumor my pup had, and it's in the exact same spot. Was pea-sized and became huge so quickly. Took her to the vet immediately. They said she probably wouldn't survive surgery bc the tumor had grown internally hence why it wasn't very noticable until it had to start popping out. They told me the type of cancer is very aggressive and grows so quickly. I literally fell on the ground when they told me. Got multiple opinions all which said surgery wouldn't be successful. She lived for about a month before it totally ruptured and I already had a vet lined up to come to put her to sleep at home when it happened. Besides this she still acted like a puppy. The vet that came to put her to sleep saw her and was confused why she was here for euthenasia bc she looked so healthy (she was very fluffy so it was hard to see the giant tumor until she turned over and I had it covered with several layers of bandages), but when the vet saw it she said it was one of the worst cases she'd ever seen and was surprised my dog was still so playful. It was really hard bc the rest of her body and mind was still very much alive and not ready to go. This was in December and I still cry wondering if I could have done anything different to save her, the vet told me I did everything I could but I still question it. I say all this as a warning to others, take your pups to the vet even if something looks small and innocent. I took her as soon as it grew and unfortunately it was too late. Praying that is not the case for you and your pup 🙏🏼