Outcomes of the transformation to diffuse large B-cell lymphoma in hodgkin lymphoma and indolent B-cell non-Hodgkin lymphoma: a population-based study.

Histological transformation (HT) to diffuse large B-cell lymphoma (DLBCL) can occur in both Hodgkin lymphoma (HL) and indolent B-cell non-Hodgkin lymphoma (B-NHL), typically associated with poor clinical outcomes. However, following the introduction of rituximab, the prognosis of transformed DLBCL (t-DLBCL) has shown considerable variability across studies. This study aimed to evaluate the outcomes of t-DLBCL originating from HL and indolent B-NHL, and to compare survival rates between t-DLBCL and primary DLBCL (p-DLBCL). Data were extracted from the Surveillance, Epidemiology, and End Results (SEER) database to identify patients diagnosed with primary HL or indolent B-NHL between 2000 and 2021, and those diagnosed with p-DLBCL during the same time. A total of 3,508 cases of t-DLBCL were identified. Compared to patients without HT, those with HT exhibited significantly worse survival outcomes. The post-transformation survival (PTS) rates at 5-year were 49.4%, 49.4%, 46.2%, 31.4% and 26.4% for t-DLBCL originating from HL, follicular lymphoma (FL), marginal zone lymphoma (MZL), lymphoplasmacytic lymphoma/Waldenström macroglobulinemia and chronic lymphocytic leukemia/small lymphocytic lymphoma, respectively. Factors such as age at HT, sex, marital status at HT, disease stage at HT, initial therapy prior to HT, and treatment regimen at HT were significantly associated with the prognosis of t-DLBCL. Notably, the PTS of specific subgroups of t-DLBCL, including patients younger than 65 years originating from FL with radiotherapy prior to HT, and those originating from MZL with either "watch and wait" or radiotherapy prior to HT, was comparable to that of matched p-DLBCL. Given the heterogeneous prognosis observed in t-DLBCL, treatment strategies should be tailored accordingly.