The pleomorphic cells of advanced mycosis fungoides. An ultrastructural study.

Five patients with advanced disseminated mycosis fungoides were studied, using light and electron microscopy. All had lesions with large pleomorphic cells by light microscopy. In three of the patients, nonlymphoid tissue was studied, including pericardium, epididymis, and small intestine. All areas selected for ultrastructural study showed large pleomorphic cells. We conclude that these represent poorly differentiated lymphoid cells derived from Sézary lymphocytes. This is based on nuclear and organelle similarities between the Sézary and pleomorphic cells, as well as the demonstration of intermediate forms.