CA15-3 marker

My oncologist keeps asking for these CA15-3 tumour marker tests, although my nurse consultant says they are not that reliable and scans are more reliable . However, my CA15-3 has gone from 101 in November to 202 in January which is a doubling in three months and seems very high . I am on cycle seven of Ribociclib and fulvestrant . My October and January scans were stable so I am feeling very confused. I’m wondering whether anybody else has come across this apparent discrepancy between what the blood test is doing and what the scans are saying. My nurse consultant admits there us a disconnect between the tumour marker and scans

I agree with your specialist nurse that most of the cancer blood test markers are not very specific or accurate, which raises the question of why are they used.
I think like many things in medicine the blood results need interpretation by a skilled health care professional alongside the clinical picture and any other available investigation e.g. imaging.
I’ve certainly learnt that although I love the hospital and NHS app where I can see all my results the interpretation of them by me is often wide of the mark, which causes me unnecessary worry. Double edged blade I guess.

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Thank you for that. I have an oncologist who I think is more likely to put weight on the tumor marker but a very skilled nurse consultant who doesn’t rate it and is more likely to encourage me . I do sometimes wonder whether they don’t agree on quite a lot!Ah well

Tumor markers are not reliable. NCI centers in the US (national cancer institutions) don’t use them for early stage diagnoses as a result. If you’re in chemo they could be going up because of inflammation somewhere. I’m not sure why you would be tested for that during chemo. Seems to be asking for unnecessary worry and strife.

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@Gillmary - I was also told by my onc that CA 15-3 marker tests are not reliable. Was told that inflammation can cause the reading to go up. I have read that a high reading does not necessarily mean cancer is back. I only had mine done twice; with each test, the reading went up but my onc assured me that there’s nothing to worry about. Hope this helps. Siggi.



As with most things when it comes to the management of 2nd Stage Cancer all the tests need to be condidered as a holistic view. I’ve also ready that the CA-153 marker is not reliable enough to form a clear view if what is happening.

CT is I think the primary data source you’re oncologist will look at.

Hope that helps and the Ribociclib Fulvestrant combination continues to work for you.

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Hi there, have posted on here before on this (others have been worried about this too). The marker was included in my regular blood tests during chemo. I freaked out once because it had gone from 20 odd to 60 but I had a cold or infection at the time and it made the marker go up. Also I went to a different lab for the test (they use different methodologies apparently). Since then it has come back down again. As others have said it is a marker so part of the toolbox they have but not reliable by itself and especially just one reading. It needs to be reviewed over time and by the medical team. One oncologist told me they shouldn’t really include it as it worries patients.

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I can relate to this and you have my full sympathy. My Onco tells me to ignore my markers one visit and when they start slowly creeping up starts ordering scans, so I understand. My markers were originally 70, dropped to 38 and have slowly crept up to 81, but slowly dropping down again. Mind you this is after having pneumonia and then Covid. I find listening to my breast care nurse is a great help, she puts it all into perspective and sorts out the confusion and fear that always seems to follow my Onco visits.
You mentioned taking Ribociclib and fulvestrant. How are you tolerating them? no problems I hope.
Stay positive and big hugs.

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