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In a 60-person phase II trial, CD38-targeted zirconium-89 daratumumab PET/CT and standard FDG PET/CT detected disease at similar overall rates. Each scan found disease or additional sites missed by the other, suggesting the tracer could complement current imaging; its role in treatment decisions and patient outcomes remains unestablished.
A phase II trial of 60 people with multiple myeloma found that a CD38-targeted PET/CT tracer detected disease missed by standard imaging in some patients, although it did not improve overall detection rates. The findings suggest the experimental scan could complement standard FDG PET/CT, rather than replace it, according to researchers reporting in Radiology.
The tracer, zirconium-89 (89Zr) deferoxamine-daratumumab, targets CD38, a protein found on the participants’ myeloma cells. Compared with standard fluorine-18 fluorodeoxyglucose (18F-FDG) PET/CT, it detected disease in 43% of participants, versus 47% for the standard scan; the difference was not statistically significant (P=0.81).
The scans nevertheless showed complementary findings. The CD38-targeted scan showed disease in 13% of participants whose standard scan did not, while FDG PET/CT showed disease in 17% whose CD38-targeted scan did not. The CD38 tracer identified more disease sites in 28% of participants; standard imaging identified more sites in 22%. The scans found similar amounts of disease in the remaining participants.
The prospective, two-center trial enrolled 60 people with pathologically confirmed CD38-positive myeloma. Participants had at least one lesion visible on CT, MRI or FDG PET/CT within 90 days before enrollment and were preparing to start first-line treatment or a new treatment line. Their median age was 63, and 53% were women. Researchers reported no severe adverse events with the experimental tracer; non-severe events occurred in 5% of participants during administration of non-radiolabeled daratumumab.
How the Two Scans Differ
The results point to a potential gap-filling role for CD38-targeted imaging: a scan may show lesions that another method misses, which could affect how clinicians map disease before treatment. The trial did not establish that using both scans improves treatment choices, patient outcomes or survival, so any clinical benefit remains to be demonstrated.
Multiple myeloma can occur in scattered sites throughout the body. If an imaging method misses some disease, clinicians may have an incomplete picture of its distribution. The study’s findings support further work on whether combining molecular imaging with existing methods can provide useful additional information for staging or treatment planning.
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Why Target CD38 in Imaging
Standard FDG PET/CT uses a radiolabeled form of glucose to identify areas of uptake. The study authors noted that myeloma cells can have low glucose uptake, limiting the usefulness of this approach in some people with plasma-cell disorders. They cited prior evidence that standard imaging can miss disease in 30% to 50% of patients with established bone lesions.
Immuno-PET pairs an antibody that binds a specific target with PET imaging. Here, the antibody is daratumumab, which targets CD38; daratumumab is also used as a myeloma treatment. The study authors said the approach is intended to combine the antibody’s target specificity with PET’s ability to map and quantify findings across the body. An accompanying editorial noted that a positive scan might have treatment relevance because daratumumab is a therapy, but the trial did not establish that a scan predicts whether the drug will work for an individual.
“This study demonstrates that immuno-PET targeting CD38 can identify, localize, and quantify myeloma, which is overlooked by FDG PET in many patients.”
— Gary A. Ulaner, MD, PhD, of the University of Southern California, speaking to MedPage Today
Limits of the Trial Evidence
The study involved 60 participants at two centers, all with confirmed CD38-positive disease and a visible lesion on prior imaging. It does not establish how the tracer performs in a broader population, including people whose disease is harder to confirm or whose lesions are not already visible on other scans.
Neither scan detected more than half of the disease present in patients with histologically confirmed disease, according to Choyke’s editorial. It is also unclear whether the additional findings change care or improve outcomes. The report does not establish the tracer’s place in routine practice, its performance alongside liquid biopsies, or whether a positive scan predicts response to daratumumab.
Testing Its Role in Patient Care
Further studies will need to test whether CD38-targeted immuno-PET adds clinically useful information when paired with standard imaging and other disease assessments, including the highly sensitive liquid biopsies discussed by Choyke. Researchers and clinicians will also need evidence on whether scan findings alter staging or treatment decisions and whether those changes benefit patients.
For now, the reported results provide proof of principle, not evidence for routine replacement of FDG PET/CT. The source report does not specify a next trial or a timeline for clinical adoption.
Key Questions
What did the phase II trial find?
The CD38-targeted scan detected disease in 43% of participants, compared with 47% for standard FDG PET/CT, with no statistically significant overall difference. Each scan also found disease or additional sites that the other did not.
Does the new tracer replace standard PET imaging?
No. The findings suggest the two scans may provide complementary information. The trial did not show that the CD38-targeted tracer is a replacement for standard FDG PET/CT.
How many people took part?
The prospective, two-center study included 60 people with pathologically confirmed CD38-positive multiple myeloma. Their median age was 63, and 53% were women.
Was the tracer associated with severe adverse events?
Researchers reported no severe adverse events with 89Zr-DFO-daratumumab in the trial. Non-severe adverse events were reported in 5% of participants during administration of non-radiolabeled daratumumab.
Is the tracer ready for routine use?
The reported study does not establish routine clinical use. More evidence is needed on whether the additional imaging findings change treatment decisions or improve patient outcomes.
Source: medpagetoday.com
