68Ga-Pentixafor PET/CT in the evaluation of post-treatment response for Waldenström Macroglobulinemia/ Lymphoplasmacytic Lymphoma

127 Objectives: Waldenstrom macroglobulinemia/lymphoplasmacytic lymphoma (WM/LPL) is an indolent lymphoma. This study is to investigate whether 68Ga-Pentixafor PET can be used to assess the post-treatment response of WM/LPL. Methods: Study Design and Patients: This is a prospective study approved by the Institutional Review Board of Peking Union Medical College Hospital (protocol ZS-1113). 18F-FDG and 68Ga-pentixafor PET/CT were performed before and after treatment. At the same time of repeated PET, clinical response is evaluated according to the IWWM consensus-based uniform response criteria for WM1-2. Imaging analysis Two experienced nuclear medicine physicians visually assessed the PET/CT images and were in consensus for the image interpretation. For quantitative analysis, we measured the total glycolysis/uptake(TLG) of bone marrow and extramedullary lesions on FDG and 68Ga-Pentixafor PET/CT with the procedures described before3. The percentage of change in TLG,serum M protein and IgM between baseline and posttreatment was calculated as ∆TLG%, ∆M-protein% and ∆IgM%, respectively. Results: Clinical Characteristics 14 patients with WM/LPL (11 men and 3 women; 61.5±8.6 [range, 48-76] y old) were enrolled in the study. One patient was IgD-type WM/LPL. The median proportion of infiltrated lymphoplasmacytic cells found from bone marrow aspiration was 10.3%±20.4 (range, 2.5%-80.5%). 4 patients were classified as being at high risk , and 8 patients were at intermediate risk. One patient was classified as being at low risk. Mutation of MYD88 was found in all patients in the present study. Baseline PET/CT According to the evaluation of 68Ga-pentixafor and 18F-FDG PET/CT, all the patients showed involvement of bone marrow including axial and peripheral bone marrow. As to extramedullary disease, lymph nodes were most frequently involved(10/14). 3/14 patients showed parenchyma organ involvement including liver, spleen and pancreas. Paramedullary diseases were seen in 4/14 patients. 68Ga-pentixafor PET/CT showed superiority to FDG PET in evaluation of intra- and extra-medullary diseases. Follow-up PET/CT After Chemotherapy After treatment, 14 patients were all received follow-up PET/CT. At the timing of post-treatment PET, 2 patients were clinically evaluated as CR, 3 were VGPR, 7 were PR and 2 had progressed disease. Among the 5 patients with CR and VGPR clinical response, 4 had consistent visual response of 68Ga-pentixafor PET, while 3 of them had consistent visual response of 18F-FDG PET. Among the 7 patients with PR clinical response, all of them had consistent visual response of 68Ga-pentixafor PET, while only 3 of them had consistent visual response of 18F-FDG PET. The two patients with clinical progressed disease both had consistent visual response of 68Ga-pentixafor PET. However only one of them showed progressed disease on 18F-FDG PET (Table 1)(Figure 1). In quantitative analysis, ∆TLG% of 68Ga-pentixafor PET/CT showed a significant direct correlation with ∆IgM% and ∆M-protein% values (Table 2).Such correlation was not observed between ∆TLG% of FDG PET and serum tumor marker. With 68Ga-pentixafor PET, among the 5 patients with CR and VGPR clinical response, 4 of them showed decreased TLG with ∆TLG% over 90%. The remaining one showed decreased TLG with ∆TLG% of 86%. 7 patients with PR clinical response had decreased TLG with ∆TLG% ranging from 41% to 85%. One of the two patients with clinical progressed disease also showed increased TLG with 68Ga-pentixafor PET. The remaining one showed slightly decreased TLG with 68Ga-pentixafor PET (Table 3). In correlation analysis, ∆TLG% of 68Ga-pentixafor PET had significant correlation with clinical response (p<0.05), while ∆TLG% of FDG-PET showed no such tendency (Table 2). Conclusions: 68Ga-Pentixafor PET could be used to assess the post-treatment response of WM/LPL.