Clinical and immunomorphological characteristics of primary mediastinal large B-cell lymphoma.

Primary mediastinal (thymic) large B-cell lymphoma is an extranodal lymphoma with primary location of the tumor in the anterior upper mediastinum in fatty and fibrous tissue with or without involvement of the thymus in the malignant process. Seventy-one patients, treated at N. N. Blokhin Oncological Center in 1992-2005 with the diagnosis of primary mediastinal (thymic) large B-cell lymphoma, were examined. Morphologically the tumor was characterized by diffuse proliferation of B-lymphoid cells of different size with different configuration of the nucleus and clear sometimes "empty" cytoplasm. A characteristic sign was stromal sclerosis; islets of residual thymic epithelium were detected in some cases. The peculiarities of immunophenotype include the absence of CD10 expression on malignant cell membrane, expression of CD23 marker in 29% patients, detection of CD38 antigen in more than half of patients, absence or slight expression of HLA-DR molecules in an appreciable part of cases. The results of CHOP treatment were in general unsatisfactory: complete remission was attained in just 13 (25%) of 52 patients, partial in 11 (21%). Three-year relapse-free survival was 37% (median 6 months), total 3-year survival was 52%. On the other hand, treatment by other protocols (MACOP-B/R-CHOP) resulted in antitumor effect in all patients (complete remissions in 58% and partial remissions in 42% patients), but because of little size of the group and short period of observation we cannot consider these differences significant. Primary mediastinal (thymic) large B-cell lymphoma is an individual immunomorphological variant of extranodal non-Hodgkin's lymphoma with a characteristic clinical course and certain routes of dissemination. The methods of first-line therapy choice are MACOP-B or R-CHOP protocols.