CA19-9, CA 125, PSA, B2M and like that

I got the results of my latest CA19-9 on Wednesday. The good news is that it hasn't gone up much, but the bad news is that it has gone up (110 in October, 115 in November). This isn't a major jump, since the numbers can go up into the tens of thousands, so it has basically remained stable for the past three months.

I started wondering, though, about other tumor marker blood tests and discovered that there are a lot of them out there -- Wikipedia lists 24. They range from the most familiar, the PSA for prostate cancer, through CA125 (ovarian), CEA (colon and rectal), and B2M (multiple myeloma, CLL, lymphomas). All of these have been developed since 1965, when CEA became the first successful blood test for a common cancer.

So if we have all these great tests, how come people are still diagnosed too late?

There are problems with these tests:
* Most healthy people have at least some of all these markers in their blood, and so far it's impossible to tell which people are healthy and which have an early case of cancer.
* On the other hand, some people don't show the markers at all. About 5% of people with pancreatic cancer don't show a CA19-9. If you just went by the marker, they'd look healthy.
* Elevated markers don't always show cancer. An inflammation or other problem might temporarily raise the marker.
* The markers themselves vary from month to month in a kind of sine wave (I'm waiting for the downward swing of mine).

So why worry about the tumor marker levels at all? Basically, because except for CT and PET scans, the markers are, at least for some kinds of cancer, the best thing we have. And that, while it's better than nothing, is really frustrating.