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volunteers positive to tumor marker, but no clinical sign of health problem! - (May/10/2013 )

I saw some strange results yesterday and I don't know how to explain them. 25 out of 40 participants in a study are positive to PSA and 12 others are positive to CA19-9 tumor markers. According to the doctors, all of the participants are in good health, but they live in a high level natural radiation area (HLNRA). Google it if you don't know what it means.

My question is, could this be an experiment error? Is it possible to see a healthy person with positive tumor marker?


Do you mean they tested at levels higher than normal, that would normally suggest cancer?

It is my understanding that some expression of both of those markers would be expected in healthy individuals and that elevated levels were indicative of possible cancer (but this is not at all my field).


I don't think it's an experimental error.
First of all, how much higher are the levels than normal ? leelee's understanding is correct, there are certain cut-off values (higher than which the tumor markers are considered as elevated and thus indicate a tumor), but the extent of the elevation often plays a role. In case of PSA the value for free PSA would be interesting to know too, if it is indicated in the study.
Second, there are several factors (other than a tumor) which can induce some tumor markers - smoking can induce CA19-9, for instance. Here is a paper on non-malignant causes of CA19-9 increase:
I just wonder what was checked for (and what wasn't) when it is stated "in good health". So they try to make the point that high natural radiation increases PSA and CA19-9 ? There might be minor (possibly inflammatory) processes ongoing already which are of no clinical relevance.
Conversely, not all tumors of a certain type express the respective tumor marker at all, which is why they can only be used to control progression or remission of the disease if they were already elevated at the point of diagnosis. PSA is used for general prostate carcinoma screening, while CA19-9 cannot be used for general screening.


@ leelee, yes, they ran ELISA and if PSA level is above 4 ng/ml it is considered as positive. But I was more confused when I saw 8% of their control group are also positive to PSA. This could be because of the age of the volunteers in the control group since one of them is 90 yo. But I'm suspicious to the results anyway. It could be fake, unless this is normal in the field of oncology. And I need to ask an expert.


Oh, I found this: Read question 3. So it could be true.