ASCO Review: PET Scans as Predictors

As promised, here's the other interesting ASCO presentation about the GALLIUM trial:

"First-line immunochemotherapy for Follicular Lymphoma in the GALLIUM study: Prognostic value of PET-CT status after long-term follow-up."

It's especially interesting to me after I saw the response to the Bone Marrow Biopsy research that I posted about a few days ago. Sometimes I'm surprised at what people respond to so passionately, and the BMB post was one of those things. I think, as patients, we are interested in testing, since it's something we all have in common. We haven't all had the same treatments -- I can't tell you anything about what it feels like to get CHOP. But we all know how it feels to have a really good phlebotomist, don't we? One that takes a blood sample and does it so smoothly that we can barely feel it happening? Same for something like a BMB or PET scans. We've almost all been through them. And if you're like me, you have strong opinions about them.

Back to this ASCO presentation:

The GALLIUM trial was created to compare Rituxan with Obinutuzumab by looking a large sample (about 1200 Follicular Lymphoma patients) and comparing how they responded to R+ chemo + R Maintenance versus O + chemo + O maintenance. Look here for more on the long-term results.

The trial has been great because it's so large, and because they have been able to track all those patients over a long term (over 6 years, and still going), and look at things besides just the R versus O stuff. For example, for this study, they looked at whether or not PET scans could predict Progression Free Survival and Overall Survival.

The quick answer is: yes, it seems like they can.

The researchers gave PET scans to some of the patients (a total of 595) before they had treatment, and then right after treatments. The scans measured for Complete Metabolic Response.  A Metabolic Response is a more accurate way of measuring than a Morphological Response. With a Morphological response, the patient might have clear blood tests, a tumor that has visibly shrunk in size, etc. Could be great news, but could also be hiding something. A PET scan can measure for Metabolic Response, and even though everything looks great on the surface, the scan is sensitive enough to show that there is still some cancer lurking about.

The question is, how sensitive is it? And how useful could it be in predicting a long response?

What the researchers found was that a Complete Metabolic Response -- where the cancer was wiped out completely, according to a PET scan -- was a good way to predict PFS and OS. 63% of patients who had a CMR right after treatment had a 6 year PFS -- the cancer hadn't progressed. Only 23% of patients with a CMR had a 6 year PFS. As for Overall Survival, the 6 year OS for the CMR group was 91%, versus abou 79% for the non-CMR group.

Why does this matter?

If a patient does not have a Complete Metabolic Response, as measured by a PET scan, right after treatment, then chances are good that the cancer will come back at some point. Those patients might need to be checked on more frequently. They might have had a Complete Morphological Response, one that made it seem like everything was all clear, but the PET said otherwise.

Of course, there's no guarantee that someone with a CMR will have a long PFS (as 37% of these patients fund out), and no guarantee that a non-CMR will not have a long PFS (as was my own experience -- my PET right after Rituxan showed some disease remained, and that was over 12 years ago).

But knowing that possibility is greater, that some disease remains, might mean that the oncologist and patient decide that more frequent appointments might be useful, or that maintenance might be a good idea, or that some other kind of salvage treatment (something different to "clean up" what is left) would be useful. It's a good tool to have.

And it confirms that PET scans are useful in some situations, like right after treatment, and right before treatment. In between treatments, when things are going well? Those are less helpful, according to research.

PET scans aren't fun (I dread drinking whatever liquid they ask me to drink), but they don't suck as bad as BMBs, and they have their place. There's a cost -- lots of radiation -- but research like this that helps us understand when they are indeed useful might make the benefits worth the cost.