ASCO: PET/CT for Follicular Lymphoma

OK, one last look at the ASCO conference from what now seems like months ago, but which as actually just a couple of weeks ago.

I was going to skip over this, but I've seen a couple of commentaries on it online, so it's probably worth mentioning here:

Researchers from a number of cancer research centers presented "Prognostic Value of PET-CT After Frontline Therapy in Follicular Lymphoma: A Pooled Analysis of Central Review in Three Multicenter Studies." The researchers were trying to determine if a PET-CT scan, rather than just a CT scan, can predict Progression Free Survival (PFS) and Overall Survival (OS) in Follicular Lymphoma patients after they have had chemotherapy + Rituxan for their first treatment.

I won't get into the difference between a PET and a CT, other than to say a CT provides a nice picture, while a PET gives information about how whatever is in that picture is behaving. (See Lymphomation.org for an overview of PET scans.)

For this study, the researchers looked at the PET scans of patients from three larger studies of Follicular Lymphoma, 246 in all. (Note: This is actually a combined PET and CT scan, but I'm just calling it a PET because I'm too lazy to add the -CT.) They evaluated the scans using a 5 point scale known as the Deauville citeria, which measures how much activity the PET scan has measured. Each scan was looked at and scored by three different people. (It's worth noting that while a PET is a very scientific instrument, the way that a PET scan is interpreted can vary from person to person, which is why they had 3 people looking at each scan.)

What they found was the PET scans were predictive of PFS and OS. That is, if a scan was deemed "negative" (little or no cancer), then PFS and OS were likely to be higher -- the disease would take longer to return, and the patient would live longer. On the other hand, a postive PET scan (evidence of cancer, or an increase in cancer) meant a shorter time before the cancer returned, and a shorter survival.

The value of a PET scan right after treatment, then, is in predicting how well that treatment was likely to hold.  The researcyhers suggest that a PET at this time should be the "new gold standard for response assessment," though they also say this evaluation should be repeated to make sure it really works as well as it seems to work.

A few thoughts on this.

First, and most importantly, looking at the numbers, it would be easy to slip into panic about this, and think that a bad PET after treatment is over means that things are hopeless. Not so. In fact, if these researchers are right, it should be cause for hope, because the PET is should be considered a "platform for response-adapted therapy." In other words, the PET can show very early whether or not a new treatment will be needed. Less waiting around and wondering if it worked, and more time to take action.

On the other hand, despite the researchers optimism, this does seem like a fairly limited study. It looks at a particular group of patients -- first treatment with chemo + Rituxan. That leaves out people who have had straight Rituxan, as well as those who have had other Cool New Treatments. I don't know if the resukts would be different with Rituxan-only patients, or, as the reserachers noted, those who went on to have Rituxan Maintenance. As they say, some further study would be helpful before we consider this a "gold standard."

I think it's also worth bringing up, again, that PET interpretation isn't an exact science. While the study used 3 independent readers for each scan, most of us in the real world get one reader, unless we ask for second and third opinions. So unless the scan is so obviously full of cancer that everyone would agree on a score, I think it might not be as neatly predictive as they think.

All that said, the big takeaway is a positive one -- we're better off with a PET than a CT scan after initial treatment, because it will tell us more.

And I say this knowing full well that I am going for a CT scan, and not a PET, in a week.

Maybe I'll write about that some more after I get the results.....