PET Scans and Prognosis for FL

The Lancet Oncology just published an article on the value of PET scans after treatment. It's called "Prognostic Value of End-of-Induction PET Response after First-Line Immunochemotherapy for Follicular Lymphoma (GALLIUM): Secondary Analysis of a Randomised, Phase 3 Trial."

The GALLIUM trial looked at Obinutuzumab, a monoclonal antibody, and how well it worked when compared to Rituxan. You can refresh your memory about it here.

In this study, the researchers looked at the GALLIUM data in a different way. They wanted to know how well a PET scan can predict prognosis. In other words, does a good PET scan (compared to a CT scan) mean a patient can expect a longer Progress-Free Survival?

The GALLIUM study looked at 1202 FL patients, divided into two groups. One received Obinutuzumab + chemo, and the other Rituxan + chemo. All of the patients were receiving their first treatment.

A smaller number -- 595 -- were given PET scans before treatment, and then again after treatment was finished. A committee (not including the researchers) looked at the PET results and decided if patients had a Complete Response or Partial Response.

The researchers and the independent committee used two different ways of analyzing the PET scans. (I don't think it's all that important to explain the difference here -- they used two ways to kind of double-check their results.)

Using the first way, at the end of treatment, 390 patients had a Complete Response based on the PET scan. Using the second way, 450 had a Complete Response.

Here's where the important part comes in.

The researchers then looked at Progression Free Survival (PFS) after 2.5 years.

In that first way of analyzing the scans, those patients whose scan showed a Complete Response had an 87.8% PFS. Those that didn't show a CR had a 72% PFS.

In that second way, patients with a CR had a 2.5 year PFS of 87.4%. Those without a CR had a 54.9% PFS.

So what does all of this mean?

Well, first, it's important to know the difference between a PET scan and a CT scan. A CT scan basically takes a picture of your insides, kind of like an x-ray, but it can show things an x-ray can't show -- things like lymph nodes. If you get a CT scan, a doctor can see that lymph nodes are swollen.

But a CT scan can't tell you why the nodes are swollen. Could be an infection. Could be cancer.

That's where a PET scan comes in. A PET measures metabolic response -- how the body metabolizes or "eats up" a radioactive substance. cancer cells eat it up more quickly, so on a PET scan, they will glow brighter.

Now take the two scans together -- two pictures, one on top of the other. The CT will show the swollen nodes. The PET will show if there is cancer in those swollen nodes (or in other places).

So this study confirms that using a PET is more useful than just a CT. Taking a PET before treatment, and then right after treatment, the doctor can compare the glows, and figure out if there is less cancer. Or if the cancer is all gone (which would be a Complete Metabolic Response -- there's no more cancer to eat up that radioactive tracer).

So if a PET scan shows that there is a Complete Metabolic Response, chances are good that the cancer is all gone. It's a better way of measuring than a CT scan, or feeling around, or any other method.

To be clear -- there's a good chance the cancer is gone. No guarantee that it's all gone, and certainly no guarantee that it isn't coming back.

But that Complete Response was a good way of predicting that it was gone for now. And two and half years after the treatment, a large number of patients were still in remission.

And, as the study shows, if there is no Complete Response, then maybe another treatment is necessary. Or maybe another scan some time to see if the cancer is progressing.

If you've been reading for a while, you've seen my rants about PET scans. I had an oncologist (no longer my oncologist) who wanted to do a PET scan without any reason. I said No. I'm young and I don't need the extra radiation.

But doing a PET right after treatment? Well, there's good reason for that, and this study confirms that.

So don't be afraid of a PET scan. Just talk to your doctor about why you need it, and the best times to have one.