11C-Acetate as a new biomarker for PET/CT in patients with multiple myeloma: initial staging and postinduction response assessment
We investigated the potential value of 11C-acetate (ACT) PET/CT in characterizing multiple myeloma (MM) compared with 18F-FDG PET/CT. Bone marrow histological and whole-body (WB) MRI findings served as the reference standards. In this prospective study, 15 untreated MM patients (10 men and 5 women, age range 48−69 years) underwent dual-tracer 11C-ACT and 18F-FDG PET/CT and WB MRI for pretreatment staging, and 13 of them had repeated examinations after induction therapy. Diffuse and focal bone marrow uptake was assessed by visual and quantitative analyses, including measurement of the maximum standardized uptake value (SUVmax). Between-group differences and correlations were assessed with the Mann-Whitney U test and the Pearson test. At staging, all 15 patients had diffuse myeloma involvement upon bone marrow examination with 30–90 % of plasma cell infiltrates. Diffuse infiltration was detected in all of them (100 %) using 11C-ACT with a positive correlation between bone marrow uptake values and percentages of plasma cell infiltrates (r = +0.63, p = 0.01). In contrast, a diagnosis of diffuse infiltration could be established using 18F-FDG in only six patients (40 %). Focal lesions were shown in 13 patients on both 11C-ACT PET/CT and WB MRI, and in 10 patients on 18F-FDG PET/CT. Focal lesions demonstrated 11C-ACT uptake with a mean SUVmax of 11.4 ± 3.3 (range 4.6−19.6, n = 59), which was significantly higher than the 18F-FDG uptake (mean SUVmax 6.6 ± 3.1, range 2.3−13.7, n = 29; p < 0.0001). After treatment, the diffuse bone marrow 11C-ACT uptake showed a mean SUVmax reduction of 66 % in patients with at least a very good partial response versus 34 % in those with at most a partial response only (p = 0.01). PET/CT using 11C-ACT as a biomarker showed a higher detection rate for both diffuse and focal myeloma lesions at diagnosis than using 18F-FDG, and may be valuable for response assessment.