Malignant lymphomas in elderly patients. Four cases studied by immunohistochemistry and electron microscopy.

Four cases of malignant lymphomas in elderly patients are reported, along with the results of immunohistochemistry and electron microscopy. Light microscopy revealed that three cases consisted of diffuse neoplastic proliferation of medium-sized lymphocytes (diffuse) lymphoma, medium-sized cell type), while the remaining one showed follicular neoplastic proliferation of medium-sized lymphocytes (follicular lymphoma, medium-sized cell type). Immunohistochemical analysis revealed that most of the tumor cells in three cases had weak to moderate immunoreactivity for L26 and weak reactivity for IgM. Most of the tumor cells in one case showed weak reactivity for IgG. Some tumor cells in three cases had weak reactivity for vimentin, and some in two cases showed weak positivity for KP1 and PG-M1. Ultrastructural examination revealed that tumor cells in all four cases contained large nuclei with clear nucleoli and scant cytoplasm. Most of the intercellular junctions were smooth, but in one case, some areas exhibited desmosomes.