Welcome at HCM.
I have read your question.
First of all if it is a tumor
of knee should have been given a sure indication about this ,please get it checked by a professional or send me a complete report.
If your doctor is suspecting it a tumor then this is not a wise decision to wait for it to enlarge.The first step in that case should be to confirm it by a scan & then get a biopsy
from it to check about its nature.
I shall advise you to get a second opinion
Hope this will help you.
With best wishes.