Prognostic Value of FDG-PET/CT Parameters in Patients with Relapse/Refractory Multiple Myeloma before Anti-CD38 Based Therapy

SIMPLE SUMMARY: Anti-CD38 monoclonal antibody has improved the prognosis of relapsed/refractory multiple myeloma (RRMM) but some patients still experience early relapse with a poor outcome. We have here evaluated the predictive value of FDG PET/CT parameters prior to receiving anti-CD38-based therapy in RRMM cases. In 38 consecutive patients, the median PFS was 12.5 months and the median OS was not reached. The presence of >3 focal lesions (FLs) on relapse PET (n = 19) and the initial ISS were associated with both an inferior PFS (p = 0.0036 and p = 0.0026) and OS (p = 0.025 and p = 0.0098). In multivariable analysis, the ISS and >3 FLs were independent prognostic factors for PFS (p = 0.010 and p = 0.025). A prognostic score combining the ISS (1,2, or 3 points) and >3 FL (1 point) individualized an ultra-risk group (scored 3–4) with a median PFS and OS of 3.1 months and 8.5 months respectively vs. not reached for patients scored 1–2. Combined with the ISS, the presence of >3 FLs on PET could improve the risk stratification of RRMM patients. ABSTRACT: Although anti-CD38 monoclonal antibodies have improved the prognosis of relapsed/refractory multiple myeloma (RRMM), some patients still experience early relapses with poor outcomes. This present study evaluated the predictive value of FDG PET/CT parameters for RRMM prior to initiating anti-CD38 treatment. We included 38 consecutive RRMM patients who underwent a PET/CT scan treated at our institution at relapse. The median PFS was 12.5 months and the median OS was not reached. 42% of the patients had an initial ISS score of 1, 37% of 2, and 21% of 3. The presence of >3 focal lesions (FLs, n = 19) and the ISS score were associated with inferior PFS (p = 0.0036 and p = 0.0026) and OS (p = 0.025 and p = 0.0098). Patients with >3 FLs had a higher initial ISS score (p = 0.028). In multivariable analysis, the ISS score and >3 FLs were independent prognostic factors for PFS (p = 0.010 and p = 0.025 respectively), and combined they individualized a high-risk group with a median PFS and OS of 3.1 months and 8.5 months respectively vs. not reached for the other patients. The presence of >3 FLs on PET was predictive of survival outcomes in patients with RRMM treated using CD38 targeted therapy. Combined with the initial ISS, an ultra-high-risk RRMM population can thus be identified.