How long will my cat live with Fibrosarcoma?

My cat Had a lump on his back and we brought him to the vet and they took a small sample of it. They said it wasn't cancer but since it grew 3x its size in a month that it should be removed. He got surgery last wednesday , aug. 12th 09. and they took tests to check if they got all of it. They just called back on the 17th to tell us that my cat has cancer and he should see a specialist. the specialist said he had fribrosarcoma and would either need more surgery to get cancer from his bones or a radiation treatment/chemotherapy. How long would he live if we didn't do any further action on his fribrosercoma cancer? He is only 6 yrs old.