Primary lymphoma of bone: a population-based study of 2558 patients.

Background: Primary lymphoma of bone (PLB) is an extremely rare malignancy arising in the skeletal system. There is no consensus over the best definition of PLB. Most of the published articles are single-institutional retrospective studies with a limited sample size. The rarity of PLB and discrepancies on diagnostic criteria has resulted in a vague understanding of PLB.

Methods: We retrospectively analyzed the clinical characteristics and prognostic factors of 2558 PLB patients who were registered in the Surveillance, Epidemiology, and End Results (SEER) database from 1973 to 2016. Survival rates were calculated using the Kaplan-Meier method. The effects of various factors on survival outcomes were analyzed by using the log-rank test. Univariate and multivariate analyses were conducted by using the Cox proportional hazards model to determine independent prognostic factors.

Results: The median follow-up time of all eligible patients was 58 months. There seemed no sex preponderance in PLB incidence. The most involved sites are axial skeletons. The most common histological subtype was diffuse large B-cell lymphoma. The 3-, 5-, 10-, and 20-year overall survival (OS) rates were 70.70%, 65.70%, 54.40% and 39.50%, respectively. PLB patients whose primary tumor sites were appendicular and craniofacial skeletons had a significant survival advantage [hazard ratio (HR) = 0.694, 95% confidence interval (CI) 0.552-0.872; HR = 0.729, 95% CI 0.597-0.889, respectively] over those with axial skeletons as primary tumor sites. Patients with Hodgkin lymphoma, non-Hodgkin lymphoma (NHL)-mature B-cell lymphoma, and NHL-precursor-cell lymphoblastic lymphoma also had a significant OS advantage (HR = 0.392, 95% CI 0.200-0.771; HR = 0.826, 95% CI 0.700-0.973; and HR = 0.453, 95% CI 0.223-0.923, respectively). Patients with Ann Arbor stage III-IV at diagnosis were at higher risk of death than those with stage I-II (HR = 1.348, 95% CI 1.107-1.641). Chemotherapy was an independent favorable prognostic factor (HR = 0.734, 95% CI 0.605-0.890).

Conclusions: Primary anatomic site, histology type, higher Ann Arbor stage and chemotherapy were independent prognostic factors. Chemotherapy played a pivotal role in PLB treatment.