The Impact of Rituximab and Radiotherapy On Treatment Outcome of Patients with DLBCL and Skeletal Involvement

There is limited information on the role of skeletal involvement in DLBCL patients treated with rituximab.

In a retrospective subgroup analysis patients with aggressive B-cell lymphomas with and without skeletal involvement were compared with respect to clinical presentation, event-free and overall survival.

Of 3840 patients 292 (7.6%) had skeletal involvement. In a multivariable analysis of patients treated within the randomized MInT and RICOVER-60 trials, the two largest randomized trials addressing the role of rituximab in DLBCL to date, skeletal involvement was associated with a reduced hazard ratio (HR) of 0.8 (p=0.181) for event-free survival and 0.7 (p=0.083) for overall survival for patients treated without, but with an increased HR (1.5; p=0.048) for event-free and (1.1; p=0.828) for overall survival in patients treated with rituximab. This was due to the failure of rituximab to improve the outcome of patients with skeletal involvement. In the MInT trial, the 3-year EFS rates were 64% without and 63% with rituximab (p=0.680) and the 3-year OS rates were 83% without and 90% with rituximab (p=0.542). similarly, in the RICOVER-60 trial, the 3-year EFS rates were 45% without and 50% with rituximab (p=0.593) and the 3-year OS rates were 68% without and 68% with rituximab. In a Cox regression model for event-free survival adjusted for the IPI risk factors a relevant interaction (HR 1.5; p=0.056) term between rituximab and skeletal involvement was observed. In contrast to rituximab, additive radiotherapy to sites of skeletal involvement was associated with a better outcome: 3-year EFS rates were 40% without and 75% with radiotherapy (p<0.001), 3-year OS rates were 70% without and 86% with radiotherapy to sites of skeletal involvement (p=0.064). In a multivariable analysis radiotherapy reduced the risk for an event in EFS by 70% (HR=0.3; p=0.001) and by 50% in OS (HR=0.5; p=0.111).

Addition of rituximab failed, but radiotherapy to sites of skeletal involvement did improve the outcome of DLBCL patients with skeletal involvement. Radiotherapy to sites of skeletal involvement, though abandoned by many cooperative groups world-wide, is recommended in the rituximab era, unless prospective trials demonstrate that it might be omitted in cases with a negative PET after immunochemotherapy.

Dreyling:Roche: Membership on an entity's Board of Directors or advisory committees. Hallek:Roche: Membership on an entity's Board of Directors or advisory committees. Schmitz:Chugai: Membership on an entity's Board of Directors or advisory committees. Pfreundschuh:Roche: Membership on an entity's Board of Directors or advisory committees; Chugai: Consultancy.