Expert: Claes-Gustaf Nordquist, M.D. - 12/31/2007

Question
My sister was diagnosed w/breast cancer in July 05. Treated w/chemo followed by radiation, 4 months later discovered cancer metastized, 2 spots detected 1)lung 2)pectoral muscle. Since first dx, the cancer has come back three times (all in l/lung area).  Her latest PET scan has detected 10 hot spots, in l/lung, top and base of spinal cord, hip and liver.  The "hot spots" range in intensity around 4-5, but the liver is a 15.  

QUESTION:  Her doctor said the Pet Scan doesn't measure size but light intensity / brightness.  What do the pet scan numbers listed above actually mean?  If the liver is a 15, what is the range of measurement?

Answer
PET scans measure metabolic rates which are higher in cancer cells than in normal cells and also higher than in inflammations/infections. So the intensities here reflect metabolic rate while increased uptake areas to some extent reflect size of suspected metastases. The numbers show an increased uptake that may be due to cancerous growth (which in bone is usually slower, while higher in for instance the liver). To go into ranges here would go into technicalities without reference to your sister's clinical situation. Has any of her metastases also been confirmed by biopsy? If so we must consider her case a stage IV (4) and therefore no longer curable though her cancer's progress may be possible to slow down by medication etc.