As I wrote in my last column, I recently learned that I am MRD negative. There are a few different test methods to detect minimal residual disease and the prognostic value of the tests varies with the testing method employed.
In my case, after doctors withdrew a sample of bone marrow from my hip it was assessed using next-generation sequencing (NGS). As I understand the process, an older marrow sample is used to identify the DNA of my original myeloma cells. The assay then looks for that DNA sequence against millions of cells in the newly extracted marrow, in my case 2,922,325 cells. If no cells with matching DNA are detected there is no minimal residual disease and the patient is said to be MRD negative.
It is possible, however, that sequencing of the cells from a marrow sample may not detect all residual disease because myeloma can appear outside the marrow.
A PET/CT (Positron Emission Tomography)/(computerized tomography) scan is an imaging technology that allows doctors to “see” areas in the body where multiple myeloma has caused tumors in soft tissue and/or congregated in the marrow. While sensitive analysis of the bone marrow can detect MRD inside the marrow, a PET/CT can detect minimal residual disease inside and outside the marrow. This is called “imaging” MRD testing.
To perform a PET scan a radioactive sugar is injected by IV. The sugar travels in the body normally and creates a “tracer”. When the patient is scanned about an hour after injection, images of the distribution of the sugar are obtained. Because cancer cells use sugar at a higher rate than normal cells they appear as “hot spots” in the images. The PET scans are merged with the CT tomographic x-rays, cross-sectional images of anatomical structures, to show doctors with great specificity the existence and location of cancer cells.
It is well accepted that patients that achieve a deeper response to treatment are more likely to enjoy longer progression-free and overall survival. So it follows, achieving MRD negativity, the deepest response that can currently be measured, is a good prognostic predictor. While it seems logical, research last fall concluded that patients that are both MRD negative in a bone marrow assay and imaging analysis have statistically improved progression-free and overall survival.
The PET/CT is an interesting test, but generally not too uncomfortable unless you are claustrophobic or have trouble being still for long periods.
To start, I began fasting six hours before the test and couldn’t exercise in any way. Exercise “fires” up the muscles and changes the way the muscles metabolize sugars, and that would throw off the scans. Presumably eating causes a similar issue. The fasting was a challenge, but I didn’t have much trouble sitting idle all morning and watching television.
When my appointment began I was injected by IV with a radioactive glucose solution. I didn’t feel anything, but I was suspicious when the nurse pushed herself away from me as we continued our small talk. When the injection was complete I was told to relax and not move around for forty-five minutes to let the tracer fluid distribute through my body. I heard “take a nap” and I always follow directions.
I was called back to the scanning room and directed to go empty my bladder as best as possible. “Be careful not to get urine on your hands, it’s radioactive. Wash up well when you are done.” Encouraging instructions, I’m sure this is all safe.
Lying flat on my back, my head in a U-shaped pillow, the bundling process began. A large rubber strap was placed around both arms at my biceps, the weight of my arms against the strap holding them in place at the sides of my chest. My toes were similarly bound to keep my feet and my legs from rotating outward. Having my arms and legs thoroughly secured, I was swaddled head-to-toe in warm blankets. This was welcome as the room was frigid.
Now resembling a mummy, the slab I was on moved back and forth, foot to head, through the large round scanning machine. It’s a bit like being passed through the hole of a giant donut.
Before the scan started the technician explained the procedure and emphasized that if I moved we would need to start over. The scanning process was easy. I tried to relax as best I could, listened to the music in the room, and tried to ignore the desire to move around. Of course, as we started I experienced an uncontrollable urge to cough. Thankfully, about 30 minutes after we started the scans I was informed they were complete and “useable.”
I was sent home to await the results. Unlike the cellular assay, when I expected the tests to detect at least some minimal residual disease, I hoped the PET/CT would confirm the earlier MRD negative findings. The PET/CT found “No abnormal osseous or extraosseous radiotracer uptake to suggest viable myelomatous involvement.”
In other words, the doctors were unable to identify any minimal residual disease in either the assay or imaging. Time to take a breath and savor another victory in this long journey.
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Photo Credit: © 2010 Mark W Pouley
“Morning Calm” was 0ne of the first photos I captured when I recognized something special and needed to share it with others. The photo was taken very early in the morning on North Twin Lake. “Mirror” images are a common tool for photographers, showing the real and the reflected. By capturing a moment in time we get to see what the eye sees naturally as well as a fleeting hidden image seen only when the waters are calm.