Pathological Features

Grossly, the SPTPs were relatively well-circumscribed tumors and the cut surface had mainly solid and cystic degenerative areas filled with hemonecrotic material, but the tumor in case 3 showed a predominance of cystic formation and in case 4 a solid appearance.

Histologically, the tumors were composed of three architectural patterns in various proportions, namely solid, pseudopapillary and cystic. The tumor cells of the solid area were uniformly medium-sized, and round to polygonal in shape, arranged in sheets with microcystic formation. The cytoplasm was clear or slightly eosinophilic, and occasionally contained small vacuoles. PASpositive hyaline globules were present within and between the tumor cells of cases 1 and 2. A few mitotic figures were detected in case 2 and mild nuclear pleomorphism was seen in case 4. The stroma between the tumor nests had hyaline fibrous bands with scattered calcification (cases 1-4) and ossification (case 1). In the necrotic and hemorrhagic areas, cholesterol clefts surrounded by foreign body cells were seen. In case 2, the tumor invaded into the adjacent pancreatic parenchyma and lymph node metastasis was detected.

Immunohistochemically, the tumor cells were diffusely positive for vimentin, and in case 1 focally positive for a-1-antitrypsin (AAT) and neuron-specific enolase (NSE). They were positive for vimentin, AAT, and NSE in cases 2 and 3 (fig. 6). In case 4, the tumor cells were diffusely positive for AAT and NSE, and focally positive for vimentin. In addition, the tumor cells were reactive for cytokeratin (AE1/AE3) in cases 3 and 4, and synaptophysin in cases 2-4. CD10 was positive for some tumor cells in cases 2 and 3. Progesterone receptors(PgR) was positive for several tumor cells in cases 1 and 2.

Ultrastructural studies were performed in cases 1, 2 and 4. The tumor cells were connected by junctional complexes and had focally irregular microvilli on the plasma membrane. The nuclei were slightly irregular and had small nucle-oli. The cytoplasm contained relatively abundant rough endoplasmic reticulum and mitochondria. In some tumor cells of cases 2 and 4, the cytoplasm contained zymogen-like granules of various sizes (range 200-2,000 nm) and annulate lamellae (fig. 7). Also, there were a few neurosecretory granules in case 2. In case 1, zymogen-like granules could not be identified, but annulate lamellae were seen.

Flow cytometric analysis revealed hyperdiploid with a DNA index of 1.13 in case 3 without metastasis, but case 2 with lymph node metastasis was diploid. Immunohistochemical study using an antibody of Ki-67, a marker of cellular proliferation, showed a low index of tumor cells (< 1.0%) for all cases, even in case 2 with lymph node metastasis.

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