I hope you have done a bit of research on immunotherapy since your last comment. If not, Here's a brief definition from cancer.org:
https://www.cancer.org/cancer/managing-cancer/treatment-types/immunotherapy.html
"Immunotherapy is treatment that uses a person's own immune system to fight cancer. Immunotherapy can boost or change how the immune system works so it can find and attack cancer cells. If your treatment plan includes immunotherapy, knowing how it works and what to expect can often help you prepare for treatment and make informed decisions about your care."

nmd78--I hope you have been able to do some bona fide medical research and have had time to sit with your child's oncologist and ask questions. I especially hope your child is being treated at a sacoma speciality clinic. As your child is an adult, I hope they have also done some research. Although Sarcomas are rare and there is not much information available online, NEVER give up hope.