Hey there. Lumps can be either tumours or abcesses. Markus has one quite noticeable one on his side, just to the side of his belly scales.
You'll have to forgive me I can't locate any of my links right now.
When I got him he had developed it a few years prior, without any noticeable injuries. So I have always assumed it was a tumour. I haven't been able to locate a vet with a lab to have it biopsied.
He recently developed, or rather I found, two additional lumps further down. Both on his side. Very small, and feel like "grains" under the skin. His larger lump is also quite soft.
With the two newer ones... I did wonder if it may be some form of calcium deposit... but I need to do some more research and get him properly checked out.
If it is a tumour and benign, then he could be fine. But until I get something conclusive I would not breed him.
Sorry I do not have much conclusive info. If I can dig up some links I try and post them soon.
Bruce