Minimal Residual Disease and Cancer Blood Tests

 I' have two related things that I want to talk about. One's been sitting in my email inbox for a while, and the other has been sitting on my kitchen table. They both have to do with blood testing as a way to detect cancer.

The thing in my email is a story from MedPage Today called "Final Results From PATHFINDER Study of GRAIL’s Multi-Cancer Early Detection Blood Test Published in The Lancet." This one is very cool. It describes the clinical trial results for a blood test called Galleri, which may be used to detect multiple cancers, possibly while they are asymptomatic. It's the "multiple" part that is getting people very excited. From a simple blood sample, the test can detect whether or not the patient has one (or more) of several cancers. The results look very promising, especially since about half of the patients that the blood test found potential cancer in detected the cancer at stage 1 or 2, when treatment is likely to be more effective. Another promising statistic -- 74% of the cancers found were for cancers that do not have a recommended screening (the way something like breast or colon cancer has a recommended screening). 

It's not a perfect test, but it's good enough that it could be very valuable for early detection for a lot of people. It's really a first step -- signalling that something should be checked out more carefully with other testing. It's less invasive that a lot of other tests might be.

The other thing that I read recently is an article from CURE magazine. It's called "On the Lookout for Minimal Residual Disease in Leukemia." It has a similar theme -- a blood test can help detect "minimal residual disease" after treatment for blood cancer. In other words, a patient might seem to have their cancer completely cured because a PET scan isn't picking up any cancer cells. But the blood test can pick up tiny amounts of cancer that a PET scan can't, letting the doctor know that a little more "salvage" treatment might be necessary. It could take months or years for the little bit of leftover cancer to show up on a scan, so the test can find it while it is still more manageable.

Both of these items highlight the kind of "liquid biopsies" that have been making a lot of noise lately. They both work on the same principle -- they can find changes in DNA in cells that send a signal that something isn't right. 

It's kind of amazing that we're able to look at such small pieces of ourselves, and it reminds me of how far we've come in a fairly short time. I remember my own biopsy. I had surgery under general anesthesia so the surgeon could remove a lymph node in my hip for testing. I was limping for a week. (I went into work the next day even though I wasn't supposed to.) The sample went to a lab, where it was looked at under a microscope  and determined to be Follicular Lymphoma. So in some sense it was worth the trouble. But if it had come back negative, that would have been unnecessary invasive surgery.

Now, this isn't to say that a liquid biopsy would completely eliminate the need for a physical biopsy. I don't think we're there yet. Someone who took the blood test and got a result for, say, pancreatic cancer might still need a scan and a biopsy to determine what was really going on. But the test has the potential to catch that cancer early. That's a wonderful thing.

My guess is we'll be seeing more research results in the next few years for MRD testing and liquid biopsies in FL. Some might be describing new tests, some might be testing what already exists. But the technology seems to be getting better all the time. Particularly for post-treatment testing, it seems likely to be a part of our testing kit in the very near future.

Good stuff.