Role of FDG-PET/CT in Detecting Lymphomatous Bone Marrow Involvement in Patients with Newly Diagnosed Diffuse Large B-Cell Lymphoma

Abstract 5204 Backgrounds: As a bone marrow bopsy (BMB) is a painful and invasive procedure with a restrictive reliability as only a limited area of the bone marrow (BM) can be evaluated, role of FDG-PET/CT to demonstrate lymphomatous BM involvement as an alternative or at least a complementary to BMB is an area of interest. Several previous studies exist but most of them included heterogeneous types of lymphomas with various treatments. Patients and methods: To evaluate the role of FDG-PET/CT in detecting BM involvement, pre-treatment bilateral BMBs and FDG-PET/CT scans of 89 patients with diffuse large B-cell lymphoma (DLBCL) treated with standard immunochemotherapy, rituximab-CHOP were reviewed and analyzed. Uptake more than liver parenchyma intensity on FDG-PET/CT was interpreted as 'with a possibility' of involvement. The final interpretation on the possibility of BM involvement in each patient was reported after discussion among three nuclear medicine physicians and results of BMB were blinded at the time of FDG-PET/CT review. Fourteen patients (15.7%) had lymphomatous involvement based on BMB (BMB+) and 17 patients (19.1%) had the possibility of BM involvement on FDG-PET/CT (FDG-PET/CT+). Seventy-two patients (80.8%) had concordant results between BMB and FDG-PET/CT (7 patients were positive for both and 65 patients were negative for both), but 17 patients (19.2%) had a discordant interpretation (7 patients were BMB+ and FDG-PET/CT-, and 10 for BMB- and FDG-PET/CT+; table 1). Although BMB+ patients had an inferior 2-year EFS (37.0% vs. 79.8%, p < 0.001) and OS (36.3% vs. 81.0%, p < 0.001) compared to BMB- patients, no differences in EFS (62.6% vs. 72.7%, p = 0.185) and OS (59.4% vs. 78.0%, p = 0.146) were shown between FDG-PET/CT+ and FDG-PET/CT- patients. Six of 7 patients with BMB+ and FDG-PET/CT+ had a diffuse involvement on FDG-PET/CT whereas 9 of 10 patients with BMB- and FDG-PET/CT+ had a focal BM involvement on FDG-PET/CT (table 2). Six of 7 patients with diffuse involvement on FDG-PET/CT were BMB+ whereas only 1 of 10 patients with focal BM involvement on FDG-PET/CT were BMB+ (table 2). It is likely therefore that patients with diffuse BM involvement on FDG-PET/CT had higher probability for BMB+ and they might have poorer survival than those with focal BM involvement. Conclusion: The results suggest that FDG-PET/CT had a limited value to detect BM involvement in patients with DLBCL. It may not be justified to upgrade patient's Ann Arbor stage to IV according to focal hypermetabolic BM lesion on FDG-PET/CT. Until additional results on the role of FDG-PET/CT in detecting BM involvement available, FDG-PET/CT should be used as an adjuvant rather than an alternative in detecting BM involvement in patients with newly diagnosed DLBCL. Disclosures: No relevant conflicts of interest to declare.