Objectives: To assess the impact of staging 2-[18F]-FDG PET in the evaluation of bone marrow involvement in patients with diffuse large B-cell lymphoma (DLBCL) in an international multicentre study in nine countries.

Methods: All patients were submitted to pre-treatment staging with PET-CT, or CT and PET scans; the studies were performed in each participating PET centre. Clinical factors comprising RIPI and bulky disease were recorded. Bone marrow biopsy (BMB) results were compared to staging PET results. PET in bone marrow was classified as completely negative, with mild diffuse uptake (also considered negative), moderate to severe diffuse uptake and presence of focal uptake.

Results: 374 participants with median age 53.3 (range 16–84) years were recruited. Individual countries recruited between 9 and 72 (median 50) cases. No bone marrow uptake was seen in 279 (74.6%), of those 263 (70.3%) patients presented negative BMB and 16 (4.3%) patients presented positive-BMB. Of the 95 (25.4%) patients with PET-positive BM uptake, 66 (17.6%) presented focal uptake and 29 (7.8%) with diffuse uptake. Of the 16 patients with BMB-positive and PET-negative results, half were already classified as stage IV by PET due to other lesions. The real impact of BMB, regarding clinical staging, was seen in only 8/374 (2.1%) patients.

Conclusion: This large study shows that FDG-PET might replace BMB in the evaluation of bone marrow commitment in BLBCL.