Transformation of "signet ring cell" lymphoma to typical nodular, poorly differentiated lymphocytic lymphoma: light microscopic, immunohistochemical and electron microscopic observations.

Malignant lymphoma with intracellular immunoglobulins giving a "signet ring" appearance to the lymphocytes is a recently described morphologic variant with specific ultrastructural and immunohistochemical characteristics. We report a case that had this distinctive morphology when initially biopsied but on subsequent biopsy 2 1/2 years later had the typical appearance of a poorly differentiated lymphocytic lymphoma without "signet ring" cells. The same monoclonal immunoglobulin class and light chain type was demonstrated in both biopsies using immunohistochemical techniques. Rare cells in the second biopsy showed the characteristic ultrastructural findings. These findings support the concept of a continuum of cell types in malignant lymphoma, with transformation toward a cell line lacking the peculiar characteristics resulting in this unique appearance.