CA19-9 Tumor Marker Number Reliability/Accuracy Query

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CA19-9 Tumor Marker Number Reliability/Accuracy Query



My name is Hugh and my Dad has stage-4 pancreatic cancer. I have a medical query regarding the reliability of the CA19-9 tumor marker number.


I have read that the CA19-9 number can be a very reliable and accurate marker of a tumors regression, though for others it can be very unreliable and give false reports. In my research I only found the false reports were in regards to when a CA19-9 number read a high and dangerous figure when in fact, the person was completely healthy; the unreliability predominantly only when reporting a higher number than it should be, whereas my query is the opposite.


How reliable/unreliable is the CA19-9 tumor marker number if it shows a lower number than expected? Is it the same reliability accuracy percentage as if it were reporting an incorrectly high number? Or is it a much more reliable tumour marker re: regression?


My Dad's original CA19-9 number when diagnosed was approx. 30,000. At the following one, around 4 weeks later, the number read approx. 1500. 3 weeks after that, approx. 500, and the latest test was around 250.


If these are reliable and accurate figures, then this is AMAZING! It wouldn't surprise me as my Dad is an incredibly strong person and very optomistic, as are we all  🙂  However, as I have read a lot about the CA19-9 number's potential for innacuracy - though predominantly when reporting incorrectly high numbers - I wanted to query the accuracy of the marker when showing lower.


My Dad has done 7 sessions of chemo (gemcitabine) over the past 10 weeks (3 weeks on, 1 off) and has been taking a few cancer-fighting dietary additives, but that's about it. As I am aware of the life-span success rate of this chemo fighting stage-4 pancreatic cancer, I want to find out if I can believe the CA19-9 numbers and be as excited as I want to be. I can be a little skeptic and don't want false hope that might divert away from trying other treatment options beyond chemo, if the numbers are inaccurate. I really hope I can believe these numbers wholeheartedly.


Any knowledge or advice that anyone can give on how reliable a CA19-9 marker number can be, particularly when reporting a low number would be INCREDIBLY appreciated. I want to be as excited as my Dad, with him. Is there a subsequent test available to see whether the CA19-9 is an accurate marker for him?


Thank you very much for any help, I really, really appreciate it.



Valued Contributor

Re: CA19-9 Tumor Marker Number Reliability/Accuracy Query

Hello @HughB and welcome.


How's your Dad doing this week?


Just bumping this one up for you 🙂




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Super Contributor

Re: CA19-9 Tumor Marker Number Reliability/Accuracy Query

Hugh CA19.9 tumor market can fluctuate during chemo,as to the big drop in numbers,sorry I don’t know the answer,possibly the best indicator is when the latest CT scan results are known, anytime the numbers come down is much better than rising,I do know when numbers go up it is the actual percentage of rise that is well as the numbers,good luck with your Dads treatments.

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