Hi,
After testing positive for anti hu antibodies (apparently these can be a marker for cancer) my doctor has asked me to consider a PET scan as he said that this would be the definitive test. He has informed me about false positive tests and the accompanying investigations and distress. I am happy with these but wondered about the chance of a PET scan not picking something up if there is something underlying. It is not only the cost of the PET scan that concerns me (I expect they are very expensive) but also the fact that I had an unremarkable LDCT scan a few months ago. Trying to do my research I can find evidence on PETs picking up tumors that were not visible on CT, the information I founfpd was during the investigation of LEMS. This gives me confidence that the PET is much better at picking up small tumors, but looking elsewhere I can find information saying how sensitive LDCT scans are and they both seem to need a tumor size of about 1 cm to be able to pick it up. If this is the case, then surely if it doesn't show on LDCT, it won't show on PET. Any experience you have on this specific question will be well received.
Thank you,
Jim
Reply # - October 16, 2016, 07:54 AM
Hi Jim,
Hi Jim,
I'm sorry to hear of this finding. Full-dose CT scans have the highest resolution, so they would usually be most likely to find something small, easily a nodule smaller than 1 cm, more like a couple of millimeters. PET, on the other hand, detects metabolic activity, and if the nodule is small enough there may simply not be enough activity to light up on the scan. They are best used after discovery of a primary tumor to see if the cancer has spread elsewhere in the body. That is one advantage of PET, in that it images essentially the entire body. The biggest disadvantage of PET is that it picks up metabolic activity of all sorts, including inflammation and infection, so it can lead to worry about a finding that is completely benign. There are also PET/CTs, but the CT component of those scans has lower resolution than a straight CT.
Since it has been several months since you had the low-dose CT, perhaps your doctor would consider another CT, possibly a full-dose scan. If a nodule has formed or grown in the interval, it should appear on a CT. The more expensive PET would still remain an option after that.
I hope you can get answers soon.
JimC
Forum moderator
Reply # - October 16, 2016, 09:05 AM
Thanks Jim, I looked at my
Thanks Jim, I looked at my correspondence and he has suggested PET/CT. It looks like he is taking a scattergun approach looking everywhere as I dont think he convinced that we are looking at a lung cancer. I will ask him about going for a full dose scan though.
Looking around at information I found a lot backs up what you have said, I am still a bit puzzled though on the papers which were published regarding diagnosis of LEMS http://m.jco.ascopubs.org/content/26/26/4276.full
Where it states that - It is possible that some patients would have been diagnosed earlier if FDG-PET scan would have been performed at first screening
This seems to suggest that CT would be better at picking up small tumors.
Thank you for replying,
Jim
Reply # - October 17, 2016, 11:47 AM
That's interesting data, Jim.
That's interesting data, Jim. I think it shows that pretty much anything can happen with cancer. There are always unusual cases such as those in the study whose nodules were missed on CT.
I don't see a problem with going with either type of scan and given the result of the previous CT, I can understand your doctor's interest in a PET/CT.
JimC
Forum moderator