Here is the latest and hopefully final update. After the MRI that did indeed show a much smaller cyst, my orthopedic surgeon does not believe this is cancer. This second MRI was on a newer machine and better quality, and taken from a more proper position. But to be sure, I will have another MRI in a month. Given the months that have elapsed and no cancer found in the biopsy even if it was not 100% conclusive, things are looking good. My surgeon believes that some sort of trauma to the leg may have caused this cyst to form. It would be nice not to have to operate as the full recovery could be quite lengthy.