Skin tumor of T accessory cells (interdigitating reticulum cells) with high content of T lymphocytes

A case of T-accessory cell tumor of the skin in a 67-year-old man is reported. The limbs, shoulders, and face were affected, but no visceral involvement is evident 6 years after onset. Tumor cells are nonphagocytic mononuclear cells with folded irregular nuclei. Immunologically, cells were positive for S100 protein, HLA-DR, Ki-M1, Leu 3a (CD4), Leu 6 (CD1); that is, they are identical to the phenotype of Langerhans or interdigitating reticulum cells (IDCs). Birbeck granules were absent. The clinical course appears to be less aggressive than that of the reported IDC sarcomas in other anatomical sites. The similarity of our case to some cases of so-called "non-X histiocytosis" of the skin is discussed. It is suspected that the "non-X histiocytosis of the skin" reported in the literature might have included T-accessory cell tumors, especially those of IDC origin. More immunological studies on the histiocytic disorders of the skin are necessary to clarify their cytogenesis.