Diffuse large B-cell lymphoma involving osseous sites: utility of response assessment by PET/CT and good long-term outcomes.

Osseous involvement by diffuse large B-cell lymphoma (DLBCL-bone) is a heterogeneous disease. There is limited data regarding response assessment by positron emission tomography with FDG, which may demonstrate residual avidity despite a complete response. We analyzed clinical data of patients with newly diagnosed DLBCL and identified all cases with DLBCL-bone. End of treatment scans were reviewed by two independent experts classifying osseous lesions into Deauville ≤3; Deauville ≥ 4, or reactive uptake in the bone marrow (M), site of fracture (F) or surgery (S). We compared outcomes of DLBCL-bone to other extranodal sites (EN) matched on IPI features and regiment. Of 1860 patients with DLBCL (bone 16%; EN 45%; nodal 39%), 41% had localized disease and 59% advanced. Only 9% (27) of patients with initial bone involvement had residual FDG avidity at the osseous site. In half of these cases, the uptake was attributed to F/S/M, and of the remaining 13, only 2 were truly refractory (both with persistent disease at other sites). Overall survival and progression-free survival were found to be similar for early-stage nodal DLBCL and DLBCL-bone, but inferior in EN-DLBCL. Advanced stage disease involving the bone had a similar 5-year progression-free survival to nodal disease and EN-DLBCL. After matching for IPI and treatment regiments, PFS between bone and other EN sites was similar. Osseous involvement in DLBCL does not portend a worse prognosis. EOT Deauville ≥4 can be expected in 5-10% of cases, but in the absence of other signs of refractory disease, may be followed expectantly.