my cat has cancer

my cat is now 9 years old and has had a cancer lump for over a year we have taken him to the vet and they said if the lump grew it needs to be taken out. and its now joined and cant put your fingers under it. but we cant afford to get it taken out. he has really thin fur and vomites abit. he also has patches where there is no fur. but he doesnt seem that sick like he still runs around catchs rabbits and birds. but how do you know if he is in pain and how long can he live with cancer thats not being treated ?