Mediastinal lymphoma of clear cell type is a tumor corresponding to terminal steps of B cell differentiation

This article reports eight primary mediastinal tumors occurring in young adults (19 to 43 years, mean 29.4 years), predominantly female (six of eight) adults. Most patients responded badly to aggressive therapy. Progression is presently noted in one patient; five patients died 10, 11, 13, 18, and 22 months after diagnosis. No patient developed leukemia. The tumors were highly proliferative, had a diffuse growth pattern, and comprised clear cells of variable size. They could not be classified histologically, but could, however, be immunohistologically characterized as B cell lymphomas. In all cases, the immunophenotype was LC+, cALLa-, CD19+, CD20+, CD21-, Ig (surface/cytoplasm)-, and PC-1+. In addition, the neoplastic cells exhibited variable defects in the expression of HLA-A,B,C and HLA-DR and inconstant expression of other B cell-restricted/associated antigens. This combination of immunophenotypical and clinical features suggests that the mediastinal clear cell lymphoma (MCCL) is a previously undescribed type of B cell lymphoma corresponding to the terminal steps of B cell differentiation.