Solid Pseudopapillary Neoplasms

Uploaded: 2007-08-27, Updated: 2007-10-27

CLINICAL FEATURES

• Low-grade malignant epithelial neoplasm of the pancreas; 0.9-2.7% of all pancreatic malignancies;

• Primarily in women,  M:F=1:9, average 28 year-old;

• Evenly distributed in the pancreas.

GROSS FINDINGS

• Average 9-10cm, mostly well-demarcated and often grossly encapsulated;

• Cut section: Most cases are solid and cystic, small lesions may be are completely solid; soft, white-gray to yellow cut surface; degenerative cavities with friable necrotic material and areas of hemorrhage; calcifications may be present.

MICROSCOPIC FINDINGS

• The tumor is composed of non-cohesive polygonal cells that surround delicate blood vessels and form solid masses with frequent cystic degeneration and intracystic hemorrhage;

• No gland formation;

• The cytoplasm is usually eosinophilic, or clear, foamy with commonly cytoplasmic vacuoles.  Often show prominent intracytoplasmic eosinophilic hyaline globules, 1-20 µm, PAS positive and diastase resistant;

• The nuclei are round to oval and uniform, and have finely stippled chromatin and frequent longitudinal nuclear grooves. Rare mitoses and unusual pleomorphism. The nuclei are sometimes oriented away from the vessels, resulting in a zone of cytoplasm that separates the capillaries from the nuclei.

• Often degenerative changes containing foamy macrophages, cholesterol crystals and hemorrhage;

• The stroma surrounding the delicate vessels is often imperceptible, but it can be hyalinized or myxoid. Rarely can show extensive stromal hyalinization. Calcifications, even focal ossification, can be seen;

• "Blood lakes” at the periphery of the neoplasm with pools of red blood cells admixed with nests of neoplastic cells;

• Dramatic degenerative changes may be seen. True tumor necrosis is uncommon, but areas of infarction do occur;

• Neoplastic cells often infiltrate the adjacent non-neoplastic pancreas.

DIFFERENTIAL DIAGNOSES

• Pseudocysts: more common in men than women, history of pancreatitis and elevated serum amylase levels;

• Pancreatic endocrine neoplasm: speckled chromatin pattern, strong and diffuse expression of chromogranin and synaptophysin, and often express a pancreatic hormone (insulin, glucagon, somatostatin);

• Acinar cell carcinomas: almost always solid, cells more cohesive and pleomorphic, frequent mitoses, lumen formation, and single prominent nucleolus and granular cytoplasm, reactive to trypsin or chymotrypsin. In contrast, solid-pseudopapillary neoplasms usually cystic, the cells very uniform, never lumen formation, lack of mitoses, grooved nuclei, inconspicuous nucleoli, and the neoplastic cells aggregate around delicate vessels rather than lumens.

IMMUNOHISTOCHEMISTRY AND SPECIAL STAINS

• Positive: vimentin, AAT, CD10, NSE, CD56, and PR, beta-catenin (90%), cyclin D1 (75%);

• Variable expression: synaptophysin and cytokeratin (AE1/AE3, CAM5.2)

•  Negative: CK7, CK19.

ELECTRON MICROSCOPIC FINDINGS

• Numerous mitochondria, abundant RER, and some annulate lamellae;

• Complex secondary lysosomes: large membrane-bound electron-dense granules (500 to 3,000 nm);

• Neurosecretory granules: in a minority of cases

CYTOGENETIC STUDIES

• Somatic point mutations in exon 3 of the beta-catenin gene (90-100%);

• Cyclin D1 over-expression

TREATMENT AND PROGNOSIS

• Although they appear grossly well-demarcated, solid-pseudopapillary neoplasms often delicately infiltrate through the tumor capsule and into the adjacent pancreatic parenchyma;

• Surgical resection is the treatment of choice;

• The prognosis is usually excellent;

REFERENCES

• AFIP Atlas of Tumor Pathology - Fourth Series. Tumors of the Pancreas