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

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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.