PET Scan, FDG uptake, and Lymphoma Question?

When you have a PET scan, they have you drink the sugar soluable radioactive "tracer" and give you some by IV followed by a full head and body scan. I realize that an FDG value of 10 or 12 is very positive, but what if you have an uptake of only 2 or 3? My original tumor (treated with radiation) only had an uptake of 5. Now my restaging showed something in one breat with an uptake of 3. The med oncologist didn't seem to concerned, but is following up the PET with diagnostic mammograms. Wouldn't ANY FDG uptake be an indication of cancer?