MEDIASTINAL LARGE B-CELL LYMPHOMA - CLINICAL AND IMMUNOHISTOLOGICAL FINDINGS IN 18 PATIENTS TREATED WITH DIFFERENT 3RD-GENERATION REGIMENS

We report on the immunophenotype, clinical findings and response to ag gressive chemotherapy of 18 patients with mediastinal large B-cell lym phoma (MLCL). Cases were collected from a series of 286 high-grade non -Hodgkin's lymphomas (HG-NHL) which, in the period September 1988 to A ugust 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-expres sion of B-cell (CD19, CD20, CD22, Ig-associated dimer) and activation- associated antigens (CD30 and CDw70) in about 60% of MLCL cases; in co ntrast, the activation-associated antigens CD25 and Ki-27 (unclustered ) were consistently negative. This peculiar phenotype may reflect a de rivation of the tumour from a subset of thymic activated B cells. Clin ically, the patients (median age 31 years; F/M ratio 2.6) presented wi th bulky mediastinal mass (72%) associated with mediastinal syndrome i n >50% cases; disease was stage IIA in most cases. All 18 patients rec eived aggressive chemotherapy (F-MACHOP 11: MACOP-B 7). Complete respo nse (CR) was achieved in 57.1% of cases treated with MACOP-B. In contr ast, 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 regim en during the trial (CR 69.6%). This difference was still statisticall y significant after adjusting for negative prognostic factors (mediast inal mass >10 cm plus increased LDH) and suggests that F-MACHOP might not be the most appropriate regimen for this kind of lymphoma.