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False Positive Pet Scan - Has this happened to anyone else?

Posts: 100
Joined: Mar 2004

Where to begin... My dad has stage IV colon cancer (dx 05/02). In 2003, his colon lite up on a pet scan, so the oncologist ordered a colonoscopy - clean. In 2004, his colon lite up again on a pet scan along with 2 liver mets. Oncologist ordered another colonoscopy - clean and he had surgery (colon biopsied and reattached - clean). In 2005, his colon lite up on a pet scan, surgeon ordered colonoscopy - clean. Now, in 2006, it has lite up again (same spot - surgical line). He is having a colonoscopy on Thursday (10/19). I am very nervous. This time, his cea is 55; however, his recent pet scan shows spots in his liver. His cea went from 3.9 to 55.1 in 25 days. This is the highest it has ever been. We have had a rought ride this summer. 5.8 cea in June and a beautifully clean pet scan. 3.9 in september (beginning) and now 55.1 in september (end) with a not so pretty pet scan. The weird thing is that none of his other blood levels changed as dramtically (wbc and rbc). He is not cold and has more energy than me and I am half his age. Does this make sense to anyone. Are all spots on a pet scan necessarily cancer. I know for a fact that last year, he had half of his liver cut off because of two spots that lite up and they turned out to be scar tissue from previous procedures. Any advice or help is welcomed. This is the best site ever for support. I read the posts all the time to lift my spirits. Thanks so much for lending a helping hand.

vinny3's picture
Posts: 933
Joined: Jun 2006

The PET scan only gives signs of areas of increased metabolism and is not specific for cancer. However since cancer cells metabolize at a higher rate than most cells an area of increased pickup needs to be suspected for being cancer. The surgical area usually will metabolize at a higher rate although one would think that by this time that area in your dad would not be metabolizing at a higher rate. The increase in his CEA is likely due to the liver mets.The wbc and rbc are not necessarily affected by the metastatic spots unless they cause bleeding.
Sorry that you, your family, and your dad have to go through all this. It is a blessing that he is feeling good and full of energy.

shmurciakova's picture
Posts: 910
Joined: Dec 2002

I had the opposite problem. I had 2 false negative PET scans. It was not until I had nodules greater than 1cm (on my lung) that it finally showed up on the PET. The wierd thing is that your father had a liver resection and did not actually have cancer. That is the second time I have heard of that on this forum! The CEA would indicate something going on and the fact that the PET is positive would indicate that it is in the liver. Is he having his CEA run again soon? I would request that and see what it says not. That is a huge rise in a very short period of time. Additionally, considering the previous unnecessary surgery I would ask if it is possible to do a fine needle aspiration (biopsy) to the liver.
Good luck to you and your Dad!

Posts: 55
Joined: Jul 2006

I agree w/ Susan. I've never heard of a false positive, although I'm not an oncologist. My Oncologist said flase negatives are possible, but not false positives. I suppose their are always exceptions to the rules.Like Susan, My CC liver mets were not picked up by PET. My mets were confirmed by needle aspiration. A biopsy, I feel is the only way to make a cancer diagnoses.

I'm curious. How did your Dad end up with a PET scan before a colonoscopy? What tests led to a PET scan?


vinny3's picture
Posts: 933
Joined: Jun 2006

False positives and false negatives are both possible on PET scans. In your dad's case it might be wise, it the lesions are accessible to have a needle biopsy.


Posts: 372
Joined: Aug 2006

When I had my pet scan it clearly showed my tumor in the colon but it also showed some "low-grade" activity in the stomach. Both of my doctors called the stomach readings false-positives and they were not concerned. Since finishing chemo some 5 months ago my CEA has remained below 1 and the CT-scan came back clear in both areas. I'll take a false positive whenever it occurs after all even the pet-scan is not 100% reliable because it doesn't search out cancer so-to-speak it shows the metabolism of sugars and assumes the higher rate is cancer. Good Luck to you and your Dad

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