Bump on my dogs backside. Cancer? Benign?

hello vets! I need advice! About 3.5 years ago I noticed a small bump above my dogs vagina. Semi soft and round. In the last few years it has gotten bigger, more plump and sometimes bleeds. I’ve never been able to figure out how why it bleeds, maybe she did a butt scoot or something. Anyway, I’ve been told it is a few different things but have never had it aspirated and tested with a needle. I am going to attach a picture and I’d just like to know initial opinions. Is it a lipoma? Perianal Adenoma? Dermatitis? Mast cell tumor? Background on my dog: Female, 9 years old in November, Boston terrier, high energy, spayed and usually unbothered by the lump (I’m more bothered by it if it bleeds because then I freak out that I’m not doing something I should be?) I am definitely afraid it is cancer but if you all look at this and can easy identify it as something simple that can be removed, I’ll do it! If it’s cancer, I’ll be devastated that I haven’t done anything about it other than monitor it’s growth. help!!!

Hello!  I think from what you've written that you already suspect what I'm going to say;  that you can't diagnose a lump either way simply by looking at it, which is why the process of aspiration and microscopy, or removal and histology is needed.  Most of the disease processes you list are possibilities and others besides, for example polyps.  However, I definitely think that you'd be right to get this checked out before it gets any bigger. Unfortunately it's true that cancerous lumps are not painful; that the pain usually associated with cancer comes when lumps stretch or apply pressure to adjacent tissues / organs etc. Which is generally not an issue with a lot of skin lumps. Your vet is in the best position to palpate (feel) this lump and let you know how far it invades the local tissues and what the available options (do nothing / sample / remove / treat with drugs for example) and their implications are from here.  It may be true that the lump is too large to remove entirely, but they would let you know. Best of luck.