Macroscopically, the tumor was of yellow-greyish color and medium consistency.
Histologic examination of both the primary and recurrent tumors showed solid nests of tumor cells surrounded by a small rim of connective tissue. The neoplasm consisted of polygonal cells with abundant, eosinophilic, granular cytoplasm and relatively sharp cellular margins. Cytoplasmic granules were distinctly PAS-positive and resistant to diastase digestion. There was remarkable cellular and nuclear polymorphism with hyperchromatic nuclei and prominent nucleoli (Fig. 2).There were small areas of foamy cells and perivascular lymphocytic aggregates. Mitoses were rarely registered. The tumor was moderately vascularized. Frank necrosis was not evident.
Immunohistochemically, tumor cells were strongly positive for neuron-specific enolase, S-100 protein, a1-antitrypsin and a1-antichymotrypsin (Fig. 3), but negative for glial fibrillary acidic protein, vimentin, various cytokeratins, melanoma marker HMB 45, chromogranin A, synaptophysin, desmin, smooth muscle actin and hypophyseal hormones. With the proliferation marker Ki-67, 1%, and in places up to 15%, of the cells were decorated (Fig. 4). 95% of the cells were positive for p53, and up to 15% were positive for apoptosis-inhibiting protein bcl-2. The cells were negative for apoptosis-promoting protein bax, and for the epidermal growth factor receptor (EGFR).
Electron microscopy revealed a densely cellular tumor with polymorphic nuclei. The cytoplasm was almost completely filled with round, electron-dense lysosomes. A small number of mitochondria were present. Other organelles were rarely observed. Intermediate filaments were not registered (Fig. 5).