Am I being unfair?

[KDcow]

My Syrian developed a lump underneath his front leg a few weeks ago. Since then it has got alot bigger. I am pretty sure that its a tumour. He is currently 2 years and 7 months old. He is fine moving around, and even though I moved his water and food to the bottom of his cage, he still climbs to the very top level. He shows no sign of pain when being handled and is still eating both treats and food. He passes no blood in his urine.
Am I right for keeping alive? I keep putting off the idea of him being put down but I want to do what's best for him. Do I put him to sleep, or leave him be and keep on eye on him until he shows he is in pain?