Immunoblastic sarcoma of the T cell type: an ultrastructural study of five cases.

Ultrastructural studies of five T cell immunoblastic sarcomas revealed morphologic features that uniquely distinguished this variant of non-Hodgkin's lymphoma. Immunoblastic sarcomas of T cell type were characterized by large lymphoid cells with striking electron-lucent cytoplasm with few organelles. Neoplastic cells of B cell immunoblastic sarcomas (5 cases) clearly differed, in that they contained numerous cytoplasmic polysomal aggregates and long, irregular strands of rough endoplasmic reticulum, occasionally with dilated cisternae. Light microscopic features were correlated with these ultrastructural distinctions. T immunoblasts correspond to large lymphoid cells with pale to clear cytoplasm, in contrast to B immunoblasts, which exhibit amphophilic cytoplasm and/or plasmacytoid differentiation. These morphologic characteristics may be helpful in identification and classification of immunoblastic sarcomas of T and B cell types.