CEA going up, up, up....anyone?

My dad's cea level has been slowly rising since he was diagnosed with colon cancer in November. He underwent a colon resection. Of the 11 lymph nodes removed, 8 were found to have cancer in them. The surgeon believed that he had gotten out all of the tumor and saw no other lesions. My dad had a cat scan which showed no other visible lesions. His cea started out at 66 before the surgery. One month postop, his cea was up to 77. Again, next cea check was up to around 88. Another cat scan with the results being no evidence of disease. He underwent a pet scan and it showed no sign of cancer. After 12 weeks of chemo (oxiplatin, leuvocorin, 5FU), his cea had climbed to 86. At this point, he went to the Mayo clinic for a second opinion. We are at 107 on the cea test at this point in time. Mayo performed a cat scan there. The doctor reviewed the new cat scan and compared it to the original cat scan. The Mayo doctor saw an ever so slight increase (lymph nodes are still very small) in the size of some lymph nodes that are behind his stomach. My dad underwent a needle biopsy (10 inch needle) and went back a week later to find out that try as they did, they were not able to get any tissue during the test. The lymph nodes are in an almost impossible place to do surgery as they are right beside the aorta. He also went and had an endoscopy and nothing was found. He had a repeat colonoscopy to look for a recurrence and nothing was found. I am really worried with the cea continually rising. The Mayo doctor has changed his regimen to Leuvocorin, CPT-11, Avastin, and 5FU. We are now waiting for 2 months to pass to see if the cea count has gone down. We were told that it may not be such a good thing if it does, as this would probably mean that the cancer is more advanced than previously thought and that he may have been under-staged. He was originally diagnosed with III colon cancer. The doctor indicated that it could possibly be lymphoma, but as they were not able to get any cells during the biopsy he really is not sure. He did say that lymphoma is a little easier to treat than metastesized colon cancer. It is so frustrating that the cea is continuously rising. Even when he had the surgery it did not go down. My dad is still working and does not even look ill. His main complaint is being very tired. I read and read and cannot find anyone with a story like his. Most people are talking about elevated cea when the blood level is 6.2 or 4.5. I completely understand their concern. I am so scared about my dad's being like twenty times this. Is there anyone out there that has any knowledge of cea levels being so high and no real sign of tumors?