What is the treatment for synovial sarcoma?

It is not: A common dx, unlike its name, does not always occur at joints, but is lumped as a "soft part sarcoma" so it can metastasize to lungs, but unlike many sarcomas, it can also travel to lymph nodes. Resection free margins is key. Even 1 node conveys higher risk of relapse. Statistics don't help. You have a chance!

Surgery foremost: There are conflicting results on whether radiation and/or any chemotherapy protocol helps at any particular stage. If the tumor has not spread to the lungs, for most patients a 5-year disease-free survival is more likely than not. Unoperated, the disease is lethal. Good luck, and thanks for asking.