PET Predicts Survival?

Very interesting research published a few days ago in the Journal of Clinical Oncology called "Baseline Metabolic Tumor Volume Predicts Outcome in High-Tumor-Burden Follicular Lymphoma: A Pooled Analysis of Three Multicenter Studies."It has some significant implications for diagnosing aggressive forms of Follicular Lymphoma.

There have been a couple of FL issues from the last couple of months that kind of come together in this article. First, there's the issue of PET scans, which have been shown to be very useful as a baseline measure at diagnosis, and again after a treatment has been completed. Gives the doctor something to compare to.

Then there's the issue of trying to identify more aggressive Follicular Lymphoma as early as possible, so treatment can be matched up with it and the disease fought aggressively. There has been some recent research that focused on the m7-FLIPI model and POD24 -- trying to figure out of a patient is in that group that will have Progression of Disease within 24 months. There's a feeling that being able to identify an aggressive FL early will perhaps allow it to treated more effectively.

The research from the JCO is related to those things. It shows some value in using a PET scan to figure out if a patient has a more aggressive type of FL.

Now, the PETs that I get come back with a number that measures the widest point of my swollen nodes. It will say something like "One inguinal node 5 cm; two chestal nodes, 6 cm and 3 cm" (I forget what nodes in the chest are called, so I'm going with "chestal." Thoracic, maybe? I'll look it up later.) That way of measuring certainly tells you something, and if you're comparing from scan to scan, it works fine by showing that nodes are growing or shrinking.

But the researchers in this study measured nodes in a different way -- by volume. So the measure not just the widest point of the nodes, but also how long the are and how deep they are. (I had to ask my kids how to measure volume. I haven't done that since high school. Height X width X depth.) Think about it as not how much liquid all of those nodes could hold if you filled them up.

What they found was that, if you added up the volume of all of those nodes, then a total of 510 cubic centimeters was a significant number.  Higher than that at diagnosis, and the Progression Free Survival (the time it took for the disease to get worse) was less than 3 years. Less than 510, and the the PFS was over 6 years. The higher volume also predicted that progression was likely to happen within 1 to 2 years (back to that POD24 again).

(In case you are wondering how much 510 cubic centimeters is, it's a little more than half a liter, or a little more than 17 fluid ounces. So you could fit all of your swollen nodes into a Grande at Starbucks, or a decent sized bottle of Coke.)

The researchers went further and compared results to FLIPI2 scores. (See Lymphomation for a discussion of FLIP and FLIPI2.) Together, the FLIPI2 and the node volume seem to be able to predict pretty well which patients will need treatment within 24 months.

By looking at the node volume and the FLIPI2 score, they were able to create three groups of patients, based on they were to reach a 5 year Progression Free Survival. Patients with low volume (below 510 cubic centimters) and a low FLIPI2 score had a 69% chance. A high volume OR a high FLIPI2 had a 46% chance. And a high volume AND a high FLIPI2 had just a 20% chance.

It's an interesting idea. It's important to remember, however, that this is not a perfect predictor. But it might give doctors a potential tool for figuring out which patients are at greatest risk for progressing early, and maybe giving them a better chance at getting more aggressive treatment early.

Some things to think about?

That volume measurement is actually called Total Metabolic Tumor Volume, and doesn't actually involve measuring the height, width, and depth -- the volume is determined with a statistical formula that estimates how much volume is there. It estimates it very well, but it's still not a perfect measure, so that 510 might not be exact. And, of course, everyone is different. No one mathces up perfectly with the statistics.

On top of all of that, the standard measurement for nodes in a PET is still to measure that widest point. I'm not sure how much work needs to be done by someone reading a PET scan to go from a one dimensional measurement to a three dimensional measurement.

So, this information isn't going to affect your next scan, most likely.

But it could end up being very useful in the future. I like that there is so much work being done to identify patients who are at risk of early progression. Even though I'm now in that group, the more we know about a sub-group, the more we'll likely know about the rest of us, too.