Non-diffuse large B-cell lymphoma transformation from follicular lymphoma: a single-institution study of 19 cases.

Diffuse large B-cell lymphoma (DLBCL) is the most common histological transformation (HT) of follicular lymphoma (FL). Other types of HT are very rare, and their incidence, histopathology, and patient outcomes have not been sufficiently described. Here, we assessed the clinicopathological characteristics of 19 cases of non-DLBCL HT of FL in a single institution in Japan to advance the understanding of the disease. Among 889 consecutive patients diagnosed with FL between 2000 and 2018, 191 suffered HT (21%). The median follow-up period was 94 months (range = 3-225). A total of 172 patients (90%) had DLBCL transformation, whereas the remaining 19 patients (10%) exhibited non-DLBCL transformation. In the latter cases, the following diagnoses were made based on morphology, immunohistochemistry, flow cytometry, and fluorescence in situ hybridization analyses: classic Hodgkin lymphoma (7 patients; 4%); high-grade B-cell lymphoma (HGBL) with MYC and BCL2 rearrangements (4 patients; 2%); HGBL, not otherwise specified (4 patients; 2%); B-cell lymphoblastic leukemia/lymphoma (2 patients; 1%); anaplastic large-cell lymphoma-like lymphoma (1 patient; 0.5%); and plasmablastic lymphoma (1 patient; 0.5%). Epstein-Barr virus-encoded RNA-1 did not associate with HT in any of the cases tested (n = 8). Patients with non-DLBCL transformation showed poor outcomes, with a median overall survival of 13 months (range = 2 days-107 months); 10 of the patients (53%) died of HT. In conclusions, non-DLBCL transformation was observed in 10% of patients with HT from FL. Our data show that timely, accurate, and comprehensive histopathological diagnosis is needed to ensure optimal treatment and improve the outcome of these patients.