Cytology of the Mycosis Fungoides and the Sezary Syndrome.

Summary.— Nine skin biopsies and 2 lymph node biopsies obtained from 6 patients with mycosis fungoides and one with Sezary syndrome were studied. Touch smears were also made. Two main cells were found in the infiltrates: mycosis fungoides cells (MC) and histiocytes. The size of the former varied between 10 and 30 μm and consequently the smaller ones were similar to lymphocytes as viewed by light microscopy. With the electron microscope they had a similar structure to the cells described by Lutzner and other writers, with slight variations according to the size of the cell. Either of the 2 cells could undergo malignant transformation, the other cell persisting as a benign associated feature. Thus mycosis fungoides can become malignant either as mycosis fungoides by malignant transformation of the MC or as reticulum‐cell lymphoma by malignant transformation of histiocytes. Neither histological nor cytological differences can be found between the MF and the Sezary syndrome.