EMN 2021 | Standardization of PET scans for MRD in multiple myeloma

Nowadays, we are using PET/CT to evaluate response to therapy, and in particular, to evaluate minimal residual disease outside the bone marrow. The reason for this resides on the fact that in multiple myeloma, it’s possible to have a different genomic profile inside the bone marrow and in the focal lesion outside the bone marrow.

So, in particular, in patients with para or extramedullary disease at diagnosis, but also during the relapse phases of the disease, it’s possible to find a discrepancy between the bone marrow, which is completely responding to therapy, so, it’s completely negative and some residual disease outside the bone marrow in the focal lesion. So, PET/CT is the best tool to evaluate this because it’s a technique, a dual technique that has both the possibility to evaluate specially where the disease is, but also the disease metabolism, and this is what is useful at this poor person.

And the good news is that in the last years, there has been the possibility to standardize the evaluation of PET/CT in multiple myeloma patients. So now, in a routine clinical practice, we can use this new criteria. That’s are the Deauville criteria that were already in use for lymphomas. And so, referring to this very simple and standardized criteria, you can use PET/CT to clearly discriminate patients with some residual disease, which is significant for that prognosis or not.

These new criteria were evaluated in a prospective analysis of two clinical trials, and then were re-applicated in an independent perspective series of patients. So there are several experiences with these criteria that showed that, in fact, they are feasible and reproducible.

In the more recent guidelines from the ESMO, so PET/CT is still the preferred imaging technique. Of course, it is not the unique technique because we know that also MRI with diffusion-weighted imaging is useful and possible in this context. So, for sure in the future, we may have some answer whether one of the two technique is better in some situations or other. And of course, there are other techniques of evaluation of minimal residual disease outside the bone marrow, such as for example, the liquid biopsy or the mass spectrometry that are currently under investigation. So, they are currently used only within the research field.

So maybe one day we will be able to use these techniques and this test of the peripheral blood that are, for sure, less expensive and more, well, more practical in use. And so, we will see what will happen with the bone marrow and imaging techniques. But nowaday, for sure, there is a straight recommendation to use PET/CT when you want to evaluate minimal residual disease after therapy, also outside the bone marrow.