I just discovered a huge lump on my little 15ish yo yorkie/pom's rump...kind of off to side of tail on upper hip/toosh. I have noticed the last week or two, he's been holding his tail down more, which is what brought me to exploring deeper into it. I don't know if it developed fast, but I didn't notice it when giving him past toosh rubs [he loves them like a cat]. He has a lot of hair, so it could just be some thing I overlooked. I will be calling vet after weekend, but I am having a hard time not letting my anxiety get the best of me. I had a ferret years ago that had a lump on the rump and it turned out to just be a harmless mass, which the vet cut open and rinsed out. It never returned and he lived a full life. Due to age here, I don't know if I can be as hopeful it's just a harmless mass, but even if it is...he has a heart murmur and I've had a couple different vets express they won't risk him in surgery [which I am not disagreeing with]. Does anyone have any experience here or can help me have kind of an idea of what to expect?