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PET scan vs CT Scan accuracy


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Hi all,

My dad is 57, was diagnosed with locally advanced PC in May 2018 after symptoms of back and abdominal pain. His original CT scan showed a 1.9 x 3.0 x 2.7 cm mass in the head of the pancreas, with SMA and SMV involvement. His CA19-9 at diagnosis was 80.

He has had 6 cycles of modified FOLIFIRINOX. His CT scans showed no shrinkage or growth of the tumor after the first 6 cycles. We decided to get a second opinion, where they immediately suggested a PET scan, which he had not gotten up to this point. The PET scan showed no fdg uptake anywhere, including the pancreas.

We are puzzled by these results, and haven't gotten a clear answer of what this could mean. His CA19-9 was 80 at diagnosis, peaked at 342, and is now down to 55.

Is it common to get false negatives on PET scans? If a CT scan still shows a mass in the pancreas, where the PET shows nothing, do we disregard the PET?

Thanks all.

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Hi srshelly,

Your dad is a similar age to me and young to have pancreatic cancer. The further through this process I go, (I have had 7 cycles of Folfirinox), the more I realise how much is guess work and supposition when it comes to test results. My CA 19-9 marker was zero at diagnosis, in fact all my blood tests were perfect and all ultrasound scans also came back clear. It was a CT scan that picked up the tumour in the head of the pancreas, I had a subsequent biopsy on the turmour which confirmed PDAC. The last CT scan I had in A&E, you would have thought I was ready for the morgue whereas apart from an infected biliary stent I felt fine. Like your father, the tumour looked about the same as before, but I was told that a PET scan wasn't appropriate because the tumour at 3.5cm was too small.

At the moment I feel the best I have all year and decided to listen to my body rather than the doctors assuming things because I am 6 months into this journey and therefore should statistically already be dead. One thing my body has asked me to do was go vegan, this wasn't a conscious decision but my body, even with Creon, could only seem to be able to digest plant based food. The more research I have done, the more I can understand what my body was asking. Whether this is just luck I don't know, but I use a minimal amount of Creon now and no other medications, I look and feel really well. No more bloating, constipation or diarrhoea! So I guess what I am saying is trust to your instincts and keep questioning and querying what you are being told.


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PCUK Nurse Nicola

Hi srshelly,

Thanks for your post to the forum, I am so sorry to hear of your Dad’s diagnosis with pancreatic cancer.

The CA19-9 is often monitored during treatment to assess if the chemotherapy is working effectively so it’s good to see that this has dropped to 55.

In relation to your question regarding the PET scan, then yes it is possible to get a false negative. Did you have the opportunity to discuss the results with the clinical team?

Please feel free to contact us to discuss this in more detail if you would like to srshelly, you can email us or ring our support line number between 10-4pm Monday-Friday. The contact details are below.

Kind regards

Nicci Murphy

Pancreatic Cancer Specialist Nurse

Support Team

Pancreatic Cancer UK

email: nurse@pancreaticcancer.org.uk

support line: 0808 801 0707

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