Sorry for the late reply for those who'd inquired about Spike. So after a series of injected antibiotics didn't reduce the size of the lump, we decided to have the lump surgically removed. It turns out it was a soft tissue sarcoma, a type of skin tumor sometimes found in reptiles. Luckily the vet got clear margins, and it has a low risk of metastasizing. It's a low-grade tumor, and not very aggressive, but we honestly never believed it was actually cancer. SO - for others whose beardies have something that looks similar, definitely get it checked out!