PET scan reliability

Lee C · New User Joined: 19 Sep 2007 Posts: 2

Has anyone out there had any experience with false positives for nodules in the lung? I have a non-calcified nodule that has not grown in 14 months and it grew slightly (all based on CT scan measurements). I recently requested my doc order a PET and it came back as positive based on moderate metabolic activity at the nodule. It also showed a slight shrinkage over the previous scan 6 weeks earlier. Is there a chance this could be a hammartoma?

I have metastatic melanoma but have been clear for 18 months including the nodule above that had shown no growth. If I had not told the doc to do PET/CT instead of just a CT then I wouldn't be writing this now and he would have said see you in 3 months.

I am leary of the results.

Muttsmom · Posted: Wed Sep 19, 2007 5:30 pm Post subject: Re: PET scan reliability

Hi,

PET scans came pick up tumors when they are smaller then other tests, but they also do give false positives. They show any abnormal activity which includes inflammation. My thyroid lit up, and it was because the rads got my thyroid, not because of cancer. I also lit up where all my nodes were removed, 7-8 months earlier and was still healing.

Is your onco planning on doing a biopsy of the nodule? I know things have changed since I had one in Dec. of 02, but I "think" I remember hearing that the activity was on a 1-5 scale (maybe that's layman's terms they used on me) and if it was under the 5, then odds were extremely good that it was a false positive. Mine was a 3.
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drrahman · New User Joined: 01 Oct 2007 Posts: 4

Dear Sir,
I m a radiologist with nuclear medicine specialisation.
Yes, we encounter false positive a lot especially with lung nodules. You did the right thing by doing regular CT scans and finally PET when it grew slightly bigger. However, the PET showed moderate metabolic activity but the size is relatively smaller.
These findings are strongly suggestive of a benign lesion such as hamartoma or granuloma. Both are not cancers. If it is cancer, we would expect the metabolic activity to be higher and they may be other associated changes such as hilar lymph node enlargement and fluid in the lung.
If I were you, I would not worry for the moment but I will continue to do regular CT because of the history of melanoma.
Dr Rahman Laughing

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