Well . . . not good news. Cider's results are in the family of "Soft Tissue Sarcoma" and specifically she has "Hemangiopericytoma". Big words for localized cancer in the soft tissue.
The "glass half full" news is these tumors are usually slow growing and localized (don't pop up elsewhere in the body). The impact is only cosmetic at this point. She is in no pain and it currently does not bother her at all. The concern is when it becomes large and uncomfortable.
I have read numerous articles today and the experts all seem to have the same conclusion at least. Surgery is rarely able to remove the entire mass when it is located on a limb. The tumors also tend to grow back faster and more invasive than the original, after surgery. The most successful way to remove the entire mass is with surgery and 15 - 18 radiation treatments (yikes), which I am not about to put my dog through.
Still deciding what to do . . . but at this point we will monitor its size and hope for slow growth and many more happy years.