Mediastinal large B‐cell lymphoma: clinical and immunohistological findings in 18 patients treated with different third‐generation regimens

Abstract

We report on the immunophenotype, clinical findings and response to aggressive chemotherapy of 18 patients with mediastinal large B‐cell lymphoma (MLCL). Cases were collected from a series of 286 high‐grade non‐Hodgkin's lymphomas (HG‐NHL) which, in the period September 1988 to August 1991, were enrolled in a prospective multicentre trial designed to compare the MACOP‐B and F‐MACHOP regimens. Immunostaining on frozen sections revealed a previously unrecognized phenotype, i.e. co‐expression of B‐cell (CD19, CD20, CD22, Ig‐associated dimer) and activation‐associated antigens (CD30 and CDw70) in about 60% of MLCL cases; in contrast, the activation‐associated antigens CD25 and Ki‐27 (unclustered) were consistently negative. This peculiar phenotype may reflect a derivation of the tumour from a subset of thymic activated B cells. Clinically, the patients (median age 31 years; F/M ratio 2.6) presented with bulky mediastinal mass (72%) associated with mediastinal syndrome in >50% cases; disease was stage IIA in most cases. All 18 patients received aggressive chemotherapy (F‐MACHOP 11; MACOP‐B 7). Complete response (CR) was achieved in 57.1% of cases treated with MACOP‐B. In contrast, the response of the 11 MLCL treated with F‐MACHOP was poor (CR 18.2%) as compared to that of the 135 HG‐NHL treated with the same regimen during the trial (CR 69.6%). This difference was still statistically significant after adjusting for negative prognostic factors (mediastinal mass > 10 cm plus increased LDH) and suggests that F‐MACHOP might not be the most appropriate regimen for this kind of lymphoma.