Tortoise has a growth

Question
My tortoise has a growth on his leg, though it does not seem to be bothering him.It is just above his knee and is quite knobbly. Is this growth cancerous by any chance? He is an Indian Star Tortoise by the way, if that is of any help. He mostly lives in the house, marble flooring and ceramic tiles. He is fed usually leaves, like lettuce, Romaine, cabbage- all which are fine for him. Thanks for the help!

Answer
Sarah,   Could you answer a couple questions for me.....do you let him play outside and more importantly how old is he? He sounds very loved and spoiled. Do you give him a calcium supplement on his food? Also, wanted to let you know they love bok choy , mustard greens , collards, turnip greens much higher in vitamin A. I'm not telling you this lol but, my red footed loves pizza...shhhh..... but, so I can get a better idea if you could get back to me I can help you more. Tina