Found A Large Lump On My Female Cats Chest??? PLEASE Help?

She is 14 years Old and has always been a very healthy cat, she is till spending lots of time outside, making as much noise as ever and jumping to impossible places, but today i noticed a large hard lump on her chest, about the size of a ping pong ball, she wriggles and cries when i touch it and it was not their a few days ago :/ I know she needs to go the vet and she will i was just wondering if anyone had experiences with this and might know what it could be? she is spayed and has been since she was 5 months old and never had kittens :L any help would be massively appreciated