scared for my mother in law

My mother in law has had Papillary thyroid cancer which was first removed in 2000 along with her whole thyroid. Well she had a recurrence in 2010 and the mass was removed from lymph node and she had her radioactive iodine treatment again. Well at that time there was a very tiny mass that was seen but left behind. It stayed stable for about a year and grew just a little bit so in 2011 they gave her another radioactive iodine treatment. Well everything was fine until this year. She went for her follow up appt in late March and everything looked okay. Well a few weeks after her appt the mass started growing and growing fast. It went from a size of a nickle to a size of a lime in two months. Well they scheduled her for surgery really quick and removed it.  My brother in law took her for her follow up appt this past Tuesday and they told him that she developed a new cancer. He said it is sarcoma. Thats all he knows as of know. They didn't even have a path report because they are still working on it. She has been referred out to oncology and we have to wait to get answers. Is this something really bad? I don't know anything about sarcoma. I know allot about her thyroid cancer and that it usually is treated with surgery and then the iodine treatment. Just worried.