Lymphocyte transformation in patients with staged mycosis fungoides and Sézary syndrome.

Lymphocyte transformation was studied in patients with mycosis fungoides and the Sézary syndrome with particular reference to the stage of disease. Phytohemagglutinin-induced lymphocyte blastogenesis was normal in stage II, became depressed in stage III and was greatly reduced in stage IV disease. Similar abnormalities were found in patients with the Sézary syndrome once the proportion of abnormal cells in the peripheral blood exceeded 10%. It is concluded that stag III mycosis fungoides is probably a critical period in determining dissemination of the disease.