Lymphoproliferative diseases of the lung in Japan: review of thirty-six patients with an immunohistochemical study.

Thirty-six cases of primary lymphoproliferative disease of the lung, collected from hospitals in Japan, have been reviewed. Histologically they were divided into three groups: definite lymphoma (DL) showing monomorphous proliferation of medium to large cells (17 cases), small lymphoid cell proliferation (SLP) frequently containing lymphoid follicles (11 cases), and pseudolymphoma showing lymphoid follicular hyperplasia (LFH) (six cases) or mixed diffuse infiltration of small lymphocytes and macrophages (two cases). In some DL cases, lymphoid follicles were present in or near the tumors. Pulmonary lesions in SLP and LFH patients were frequently detected at their medical checkups. Immunohistochemistry revealed that proliferating cells in 15 out of 17 DL and all SLP cases were B cells with restricted expression of the immunoglobulin light chain, all lambda type, in three DL and four SLP cases. From morphologic and immunologic findings, 10 SLP cases were diagnosed as intermediate lymphocytic lymphoma (ILL) and one as being of lymphoplasmacytic type. Two DL cases with convoluted nuclei proved from immunohistochemistry to be of T-cell type, showing a much lower frequency of T-cell type than that found in the USA (approximately 50%).