incease in CEA

My Mom (72 yrs old) had surgery for polop removal in Feb. 2009. her first colonoscopy was Dec. 2008. The polop was almost blocking colon. At the time of surgery her CEA was 5.8. At the time she was smoking. Turns out she had Stage 3 colon cancer with cancer in 8 lymph nodes when she had her colon resectioned. She has 3 chemo treatments left of her 6 months of chemo. Her CEA levels have stedily increased from 5.8 to 7.8. She had a PET scan. It showed activity in colon, 1 cm nodes in thyroid and lungs. The thyroid was biopsied-not cancer. The lung specialist said imaging tests appear to be scar tissue. The oncologist did not think the activity in colon on PET scan was additional cancer. Could it be more colon cancer so soon?   Since 8 lymph nodes had cancer-can there be more colon cancer in lymph nodes away from the original site or on the outer colon wall that would not have shown up on the Dec colonoscopy? Or doesn't colon cancer work that way? Any thoughts would be appreciated.