Langerhans cells and their precursors with S100 protein in mycosis fungoides.

Twenty-four cases of mycosis fungoides and two cases of Sézary's syndrome were studied with special reference to the infiltration and proliferation of Langerhans cells stained with anti-S100 protein antibody. The number of S100+ histiocytes (Langerhans cells and their precursors) ranged from 104 to 345 (average 188) per 1,000 lymphoid cells in the erythematous and plaque stages, while it decreased to 4-71 (average 34) per 1,000 lymphoid cells in the tumor stage. Conversely, the number of lymphoid cells averaged 6 and 10 per S100+ histiocyte in the erythema and plaque stages, respectively, while it increased to 21.0 per S100+ histiocyte in the tumor stage. The mitotic index of lymphoid cells correlated with the lymphocyte/S100+ histiocyte ratio. A small number of S100+ histiocytes in mycosis fungoides indicated poor prognosis.