A comparative analysis of transformed indolent lymphomas and de novo diffuse large B-cell lymphoma: a population-based cohort study.

Histologic transformation (HT) of indolent non-Hodgkin lymphoma (iNHL) to diffuse large B-cell lymphoma (DLBCL) carries a poor prognosis. Using the Surveillance, Epidemiology, and End Results-17 database, we conducted a population-based study of adult patients with transformed follicular lymphoma (t-FL), marginal zone lymphoma (t-MZL), lymphoplasmacytic lymphoma/Waldenström macroglobulinemia (t-LPL/WM), and de novo DLBCL. Primary outcome was relative survival (RS), and secondary outcomes included overall survival (OS) and lymphoma-specific survival (LSS). Outcomes were modeled using flexible parametric survival models, while multivariable modeling was used to compare RS, OS, and LSS. The incidence of HT was highest in splenic MZL (SMZL, 6.78%) and lowest in extranodal MZL (EMZL, 1.62%). Median follow-up times were similar for patients with de novo DLBCL and transformed indolent lymphomas. The 5-year RS and OS were longer in de novo DLBCL compared to all other transformed iNHL subtypes (68 versus 59%, respectively). For t-FL, early transformation (within 2 years of diagnosis, Hazard ratio [HR] = 1.34) and prior treatment (HR = 1.89) were associated with inferior survival. This association was not observed in other transformed lymphoma subtypes. This is the first comparative study to show that the outcomes of t-LPL/WM were inferior compared to de novo DLBCL and highlights the need to incorporate early experimental therapies in patients with t-FL with early transformation and receipt of prior chemotherapy.