You need to undergo chemotherapy
I suppose amputation
is correct for a sarcoma
. Probably there were no means to preserve the limb based on the location of the tumor
The PET scan has not shown any spread elsewhere. That is a good sign.
Chemotherapy is being administered since the tumor is high grade. The utility of chemotherapy is debatable. Generally for a fit or younger patient the policy is to err on the side of administration of chemotherapy. Although the PET scan does not show any spread, there are always chances of microscopic spread of the disease which cannot be detected by any currently available investigation. Hence, in a high grade sarcoma, the chances of such undetected spread being high, the doctor would usually err on the side of chemotherapy.
The usefulness of chemotherapy would be in the range of 15-25%. Unfortunately there is no way to ascertain whether you would be in that category of usefulness or not. In addition, since there is no detectable disease, the efficacy of the drug in you cannot be evaluated.
With no detectable disease, it would be better to over-treat than under-treat as the doctor would like to give you that additional benefit in the attempt to cure. Hence, even with usefulness in doubt, it would be advisable to undergo chemotherapy.