The pancreas consists of exocrine glands, endocrine glands, connective tissue, nerves, blood vessels, and ducts.
The main "caput" part of this gland is closely attached to the duodenum with main duct, that together with ductus choledochus, opens up in papilla Vateri in the duodenum. The distal part of ductus choledochus and ductus pancreaticus runs together and becomes an integrated part of the dorsal part of the gland.
Tumors originating in the distal part of ductus choleducus, ampulla Vateri or the distal part of the panreatic gland, are often difficult to separate from each other, especially in locally advanced stages. The majority of exocrine tumors in this region are adenocarcinomas and can be differentiated into intestinal or pancreaticobiliary types.
According to an international consensus, intraepithelial ductal lesions are designated as Pancreatic Intraepithelial Neoplasia graded, I-III (short for Pan-IN I-III).
This terminology reflects different grades of dysplasia in flat epithelium in small or medium-sized ducts in the pancreatic gland, usually < 5 mm in diameter.
In the pancreatic gland without cancer, Pan-IN grade III is observed in < 5%, although, it is found in 30-50% of pancreas with carcinoma.
Intraductal papillary mucinous neoplasi (IPMN) is a primary neoplastic precancerous lesion with a varying degree of malignant potential. These are characterized by cystic dilatation of the main or secondary ducts with mucin production. IPMN is graded as adenoma (benign), borderline or carcinoma.
There are no known endocrine precursor lesions.
Classification of exocrine neoplasia
The majority of malignant tumors in the pancreas are adenocarcinomas. These originate in the middle-sized ducts within the pancreatic gland. Most of them are differentiated as pancreaticobiliary adenocarcinomas, i.e. they have a phenotype resembling pancreaticobiliary duct epithelium. The other, less frequent, intestinal type demonstrates a intestinal/colon-like phenotype.
In the locally advanced tumors in the caput part of the pancreatic gland, it can be difficult to decide whether they originate in the pancreas ductus choledochus, ampulla Vateri, or duodenum. In these instances immunohistochemistry may be helpful.
Adenocarcinoma in the pancreas has a tendency to produce fibrous connective tissue making them very hard tumors.
Intraductal papillary mucinous carcinomas usually originate in the main pancreatic duct. Also, when pronounced atypia/carcinoma in situ exists in the this tumor type, it is designated as carcinoma. The exact incidence of this tumor type is unknown, but probably accounts for less than 5% of all neoplasias of the pancreas. Malignant IPMN has a better prognosis than ordinary pancreatic adenocarcinomas.
Tumors originating in the exocrine glands are rare, and constitute 1-2 % of all acinic cell carcinoma in the pancreatic gland. Even if this tumor grows more expansive than infiltrative compared to ordinary adenocarcioma, the prognosis is poor with 5-year survival < 10%.
A solid pseudopapillary tumor (Franz tumor) is a tumor type that mainly exists in younger women. They are usually benign. Metastases have been reported in 15-20% of all patients with this diagnosis.
Serous microcystic adenoma is a tumor without malignant potential in contrast to mucinous cystadenomas.
Blastoma in the pancreas is very rare and is found usually in small children. It consists of epithelial and mesenchymal components.
Endocrine neoplasia in the pancreas is rare. Immunhistochemical markers such as synaptophysin, CD56 and chromogranin are important to diagnose these types of tumors. These tumors can produce hormones such as insulin, glucagon, gastrin, somatostatin, and vasoactive intestinal polypeptide.