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%; CD 10, 9%; BCL 6, 59%; MUM 1, 38%; MYC , 42%; BCL 2, 35%; Ki67 ≥ 90%, 23%; and CD 5, 3%. The majority (75%, 9/12) of GCB ‐type DLBCL s exhibited CD 10 − , BCL 6 + and MUM 1 − immunophenotypes; the remainder had CD 10 + 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.