The SCARLET trial: a prospective phase II study of somatostatin receptor imaging for potential radiotheranostic application in patients with relapsing and refractory multiple myeloma.

PURPOSE: This phase II study investigates the expression of somatostatin receptors (SSTR) in relapsing and refractory multiple myeloma (rrMM) patients for potential radiotheranostic application.

METHODS

Seventeen triple-class exposed rrMM patients who demonstrate [18F]F-FDG avidity were prospectively included. Patients underwent a [68Ga]Ga-DOTATATE PET/CT within 4 weeks after [18F]F-FDG PET/CT, which was performed as part of the standard workup. Focal lesions (FLs) were identified on both scans and were defined as focal uptake higher than the femoral bone marrow background uptake. Peptide Receptor Radionuclide Therapy (PRRT) eligibility was determined based on the following criteria: absence of [18F]F-FDG-avid FLs without corresponding [68Ga]Ga-DOTATATE uptake, identification of ≥ 3 [68Ga]Ga-DOTATATE FLs, and no diffuse bone marrow uptake on [68Ga]Ga-DOTATATE PET/CT.

RESULTS

All patients had measurable disease on [18F]F-FDG PET/CT. [68Ga]Ga-DOTATATE uptake was observed in all patients, with FLs identified in 15 of the 17 patients. The combined [18F]F-FDG and [68Ga]Ga-DOTATATE PET/CT analyses classified patients into 4 categories: (1) Identical FLs identified by both radiotracers; (2) All [18F]F-FDG FLs showed corresponding [68Ga]Ga-DOTATATE uptake, with additional [68Ga]Ga-DOTATATE FLs; (3) Only some of the [18F]F-FDG FLs showed [68Ga]Ga-DOTATATE uptake; (4) Diffuse bone marrow uptake of [68Ga]Ga-DOTATATE, preventing FLs identification. Patients in categories 1 and 2 were deemed PRRT-eligible if they had ≥ 3 FLs on [68Ga]Ga-DOTATATE PET/CT. Consequently, 10 out of 17 patients (60%) met the PRRT eligibility criteria.

CONCLUSION

In heavily pretreated rrMM patients showing avid disease on [18F]F-FDG PET/CT, [68Ga]Ga-DOTATATE PET/CT identified 60% of patients as eligible candidates for PRRT, suggesting a potential new indication for PRRT in selected patients.

TRIAL REGISTRATION: NCT04379817, Registered on 4 May 2020, https://clinicaltrials.gov/study/NCT04379817?cond=multiple%20myeloma&term=scarlet&rank=1.