Indeterminate cell tumor of the spleen.

Indeterminate cell tumor is an extremely rare neoplasm that mainly occurs in the skin. We report a case of indeterminate cell tumor arising from the spleen, a previously unreported site for indeterminate cell tumor. Histologically, the tumor showed nests, nodules, and sheets of large polygonal cells with mostly oval nuclei; open chromatin; variable nucleoli; and abundant, eosinophilic cytoplasm. Some cells possessed irregularly convoluted nuclei with nuclear grooves and granular cytoplasm, suggestive of Langerhans cells. Immunohistochemically, the tumor cells were diffusely positive for S-100 and CD1a and negative for Langerin. No Birbeck granules were found by electron microscopy. Clinical and radiologic examination showed no other organomegaly or lymphadenopathy. A diagnosis of primary indeterminate cell tumor of the spleen was rendered. To the best of our knowledge, this is the first indeterminate cell tumor reported in the spleen. Biologic insights into dendritic cells in the spleen and the pertinent literature on these entities are reviewed.