Does a change in CA19-9 indicate change in tumor?

Based on anecdotal evidence I would say not necessarily is there a direct correlation between size of tumor and percentage increase in CA19-9. You would first have to at least rule out that there are no new metastases that might be responsible for the increase.

Agreed. CA19-9 is not an absolute indicator for all people. In fact, trials are working diligently to provide a BETTER test that works for all.

I have observed that over 32 months of this, it is the trend line that counts. During chemo, it’s tested every time so easy to plot, which I have done.
Also, the lab it is tested in makes a difference.
It can indicate emergence of new tumors or growths of existing ones.

CA19-9 is not specific to PDAC cancer. There are many things that can afrect its value both benign and malignant. CA19-9 is affected by inflammatory processes of which a patient might not even be aware of another underlying pathology at play such as a sub-clinical Covid infection. This is why an oncologist will never make a treatment decision based on a CA19-9 value. If an upward trend is observed, it would trigger an oncologist to perhaps do a scan at 2 months rather than wait three months.

It is the comparison of index tumor(s) in a prior scan to a current scan that is used in basing the treatment decision. It is practical to use CA19-9 in association with tumor size. Far too many variables can effect it from genetics to certain products containing Biotin (Vitamin B-7 and even a report of excessive tea consumption causing a rise in CA19-9 but no tumor or a tumor shrinking.. This phenomenon is well documented and published. Don’t get obsessed with the CA19.9 value.

RISES IN CA19-9 at start of chemo
https://www.sciencedirect.com/science/article/pii/S2468294221000952

thanks for the good info

If a couple doctors had gotten obsessed with my CA19-9 values, I might be cancer-free now instead of stage-IV with a feeding tube.

You are correct that it must be accompanied by other supporting data. Elevations or rising trends should be investigated promptly and seriously.

Although there are many benign causes, PDAC (initial diagnosis, progression, metastasis) is among the worst possible causes, and thus deserves to be ruled out first.

My multi-year set of biweekly CA19-9 data has been a pretty reliable indicator/predictor of chemo dose changes/effectiveness and disease progression -- cheaper and earlier than ctDNA and imaging (which later confirmed what CA19-9 had been "suggesting" all along).

Yes, agreed. With sine mutations CA19-9 is a very good indicator of cancer spread. I have ATM mutation and my drs agreed it’s a very good indicator for me. It can fluctuate with inflammation or decrease of chemo levels in your system. I’m proud to say I’m obsessed with my ca19-9 and it’s why my oncologists continually remark “well we’ve caught it (the spread) very early”. It’s a balancing act not to be full of anxiety when those numbers go up, but it also can be one of the quickest and cheapest tools you can use in your arsenal to fight this disease. My suggestion is to fill your time with stuff you enjoy in order to mitigate that anxiety when those numbers go up, and please press your drs to get the imaging that might verify the rise in CA19-9.

I too have become obsessed with my CA-19, but repeatedly told by doctors to relax. Do you worry about fluctuations within normal range (< 37)? I was 174 at diagnosis, hit 450 with 2nd round of FOLFIRINOX, switched to Gem/Abrax and immediately dropped to 75. Then been under 37 since. Had surgery July 2023. I was at 11 before surgery, but ever since have been moving between 17 and 30 with ups/downs.

Dittos! I have a spreadsheet where I have recorded my CA19-9 since diagnosis. (11/2021)
For me, it is definitely indicative. My oncologist agrees. I would love to know if it has to do with my mutations or some other chemical make up. But I can now see that a tumor soon began to form when the abraxane was removed from my “recipe” . On a clinical trial now and yes, I am also obsessed with knowing my CA19-9. I’ll be calling in a few hours!!

Ashley2235,
I believe gamaryanne stated at one time (at least) that it’s the trend. Is there a trend of ca19-9 going up? My transition into stage 4 occurred 4 months after I completed chemo and my ca19-9 was 24. My CA19-9 was 6 when I had originally had completed chemo. Just 2 weeks before my CT scan was clear. Imaging can be months behind the elevation of your tumor marker. My tumor marker continued to escalate and by the time my imaging (I asked for an MRI instead of a CT based on comments from this site) and endoscopy/biopsy validated the spread to my liver my tumor marker was at 3840. It’s good to know your mutations, and then speak with your oncologist on whether ca19-9 is a good indicator for you.

Unfortunately I don't have any mutations. How much time passed between your increasing CA19 for metastasis? My value has gone from 16 to 30 (with a couple down fluctuations) between November 2023 and September 2024.