Clinicopathological features of histological transformation from extranodal marginal zone B-cell lymphoma of mucosa-associated lymphoid tissue to diffuse large B-cell lymphoma: an analysis of 467 patients.

This study analysed incidence, patient outcome, immunophenotype and prognostic factors of histological transformation (HT) from extranodal marginal zone B-cell lymphoma of mucosa-associated lymphoid tissue (MALT lymphoma) to diffuse large B-cell lymphoma (DLBCL) in 467 patients (median age, 61 years). The primary sites of MALT lymphoma were the stomach (43%), ocular adnexa (25%), lung (8%), systemic (8%) and other tissues (16%). HT occurred in 8% of MALT lymphomas. Risk of HT by 15 years was 5%: 4% in limited-stage diseases (n = 385) and 16% in advanced-stage diseases (n = 56) (P = 0·02). The median time to HT was 48 months (range, 4-139). Five-year progression-free survival (PFS) and overall survival (OS) rates after HT were 80% and 94%, respectively. Immunohistochemical results of DLBCL were as follows: germinal centre B-cell (GCB)/non-GCB, 37%/63%; CD10, 9%; BCL6, 59%; MUM1, 38%; MYC, 42%; BCL2, 35%; Ki67 ≥ 90%, 23%; and CD5, 3%. The majority (75%, 9/12) of GCB-type DLBCLs exhibited CD10(-) , BCL6(+) and MUM1(-) immunophenotypes; the remainder had CD10(+) immunophenotypes. Multivariate analysis revealed that only advanced stage at HT was a significant adverse factor for PFS (P = 0·037). Thus, overall risk of HT was low and prognosis after HT was favourable; however, in advanced-stage cases, risk of HT was relatively high and prognosis was unfavourable.