I had positive pet scan years ago ( follow up from findings on chest Xray after pneumonia) and a top Dr in Phila advised to wait and watch - said it could be mold. (I avoided major lung surgery as was advised by other drs/surgeons) - watched it with periodic scans - stable - no changes for years - fast forward to now - I have MAC and possibly Aspergillus (mold) - found MAC accidentally via coronary calcium scan . No symptoms except very mild congestion. So Dr was right about the mold....