SOLITARY FIBROMASTOCYTIC TUMOR ARISING IN AN INGUINAL LYMPH-NODE - THE FIRST DESCRIPTION OF A UNIQUE SPINDLE-CELL TUMOR SIMULATING MASTOCYTOSIS

A 77-yr-old man presented with a right inguinal mass. At herniotomy, an enlarged inguinal lymph node was also removed. Gross examination revealed a firm gray tumorous nodule measuring 3 cm in maximum diameter. On histological examination, the lymphatic tissue was found to have been almost completely replaced by spindle-shaped tumor cells arranged in whorls and bundles. In Giemsa-stained sections, about one-third of the tumor cells were seen to be strongly metachromatic tissue mast cells. The other tumor cells reacted only with a monoclonal antibody against vimentin out of a broad panel of antibodies directed against various antigens expressed by leukocytes, mesenchymal cells, and epithelial cells. A small fraction of the nonmetachromatic tumor cells reacted with the proliferation-associated antibody MIB1. Immunostaining with an antibody against p53 tumor-suppressor gene products was negative. Electron-microscopic examination revealed mast cells containing abundant granules, which were intermingled with fibroblasts that had bizarre, elongated nuclei. No myofibroblasts, desmosomes, or basement membrane material were detected. Clinical examination revealed no abnormalities, and blood and bone marrow findings were completely normal. A diagnosis of solitary (apparently benign) fibromastocytic tumor was established on the basis of the relative tumor cell numbers, the cytological features, and the clinical data, To the authors' knowledge, this is the first description of a solitary spindle cell tumor arising in a lymph node and simulating mastocytosis.