Dermal Langerhans' cell tumor in chronic myelomonocytic leukemia.

Disseminated dermal tumors in a 71-year-old male represented the first clinical manifestation of a chronic myelomonocytic leukemia. The dermal infiltrate in one of the nodules consisted predominantly of closely packed pleomorphic Langerhans' cells (LC) with typical Birbeck granules and a strong reactivity for S-100 protein. The simultaneous presence of immature myeloid cells led to the suspicion of an underlying myeloproliferative disorder. The diagnosis of chronic myelomonocytic leukemia was subsequently confirmed by bone marrow histology and blood picture. Although some peritrabecular foci of histiocytic cells were detected in bone marrow, no LC could be identified by electron microscopy and histochemical methods. Tumorous aggregates of LC in myeloproliferative disorders have not been described in the literature. Histiocytosis X and related diseases could be definitely excluded in the present case. This case obviously suggests an interrelation between the myeloproliferative disease and the focal accumulation of LC in the dermis. In animal studies by Katz et al. LC have been shown to originate in the bone marrow, whereas the origin of LC in man is still a matter of discussion. The present case supports the hypothesis that LC in man are also of myeloid origin. The neoplastic blood monocytes could be the precursors of the dermal LC. This differentiation did not take place in the bone marrow but only in the dermis where LC occur under nonneoplastic conditions ("homing").