Clinical features, management and prognosis of multifocal primary bone lymphoma: a retrospective study of the international extranodal lymphoma study group (the IELSG 14 study).

'Multifocal bone lymphoma' or 'polyostotic lymphoma' is a neoplasm with exclusive multifocal involvement of the skeleton, without affecting lymph nodes or other soft tissues. Knowledge on this uncommon condition is limited because the related literature is sparse and fragmentary. We reviewed cases of multifocal bone diffuse large B-cell lymphoma (MB-DLBCL) registered in a clinico-pathological database of the International Extranodal Lymphoma Study Group that includes 499 cases of bone lymphoma. Clinical features, management and prognosis of 37 MB-DLBCL patients and 63 'controls' (stage-IV DLBCL and skeletal involvement) were analysed. Presentation and treatment of MB-DLBCL and controls were identical. At a median follow-up of 52 months (10-189), MB-DLBCL patients exhibited a significantly better response rate (92% vs. 65%; P = 0·002), progression-free survival (5-year: 56 ± 9% vs. 34 ± 6%; P = 0·003) and overall survival (5-year: 74 ± 8% vs. 36 ± 7%; P = 0·002). Among MB-DLBCL patients, the use of post-chemo radiotherapy was associated with better overall survival (5-year: 83 ± 12% vs. 55 ± 16%; P = 0·003). Two MB-DLBCL patients (5·4%) with spine and skull involvement experienced central nervous system (CNS) relapse. Thus, MB-DLBCL patients exhibit a significantly better prognosis compared to patients with advanced-stage DLBCL, and should be treated with conventional anthracycline-based chemotherapy, keeping intensified treatment for relapsing cases, considering involved-field radiotherapy, and CNS prophylaxis in high-risk patients.