Connie,
There are many types of sarcomas. You have to find out by getting the pathology report. If you haven't found a support group online, there are a few sarcoma groups on www.acor.org Yes, it is possible for a tumor to grow large in a short time. Low grade and high grade are treated differently. You should look for a sarcoma specialist at a sarcoma center. Here is a list of them in the US:
http://tinyurl.com/7yh3w
Best of luck,
24 year survivor of low grade myxoid LMS/ESS, stage IV for 12 3/4 years. There is always hope.