If you’ve seen an exotic specialist for a second opinion then their diagnostics should be more reliable. I had a mouse who had a mammary tumour and she caught that and they do bleed alot they often have lots of blood vessels in them. I hope your vet appointment goes well.
All vets can do is advise pts if they think it right - they cant force you to do it and they need your consent anyways through a signature on a consent form. If he acting normally and the lump is otherwise not bothering him then I see no reason for pts to be an option and the vet might give him antibiotics to stop any infections:
These thread should help with uploading photos.
How to resize photos 2018 And to embed the photo
How To Embed Photos. You need to resize them first and I use imgbb.com as a photo host as I cant upload photos from my iphone onto the forum.