Pancreas

(a) Exocrine

— ductal adenocarcinoma (80-90% of cases):

tubulo-acinar pattern of malignant ductal epithelium in a desmo-plastic stroma with perineural invasion and dysplasia of the adjacent duct epithelium (20-30%). Pancreatic intraepithelial neoplasia (PanIN) is a microscopic papillary or flat, non-invasive epithelial neoplasm (dysplasia) comprising cubocolumnar epithelial cells with variable degrees of cytoarchitectural atypia. It usually arises in pancreatic ducts <5 mm diameter, is multifocal and seen adjacent to existing carcinoma, being regarded as a precursor to it. High-grade PanIN is equivalent to severe dysplasia or carcinoma in situ. Note that PanIN can be mimicked by florid reactive atypia or cancerization of ducts by invasive ductal carcinoma. multifocality 15-40%. male preponderance.

— ductal adenocarcinoma variants:

mucinous non-cystic colloid carcinoma (1-3%): mucin in >50% of the tumour.

adenosquamous: at least 30% squamous component. microglandular/signet ring cell—poor prognosis. Exclude a gastric carcinoma secondary deposit. oncocytic. clear cell.

— undifferentiated carcinoma (2-7%: syn pleomorphic/giant cell/sarco-matoid carcinoma):

spindle cells/pleomorphic cells/mitoses/lymphovascular invasion. Variant with osteoclast-like giant cells may have a slightly better prognosis.

— intraductal papillary or mucinous neoplasms/tumours (IPMNT): IPMNT is a clinically detectable grossly visible, non-invasive, mucin-producing papillary epithelial neoplasm. It arises from the main pancreatic duct or branch ducts with varying duct dilation (>1 cm) and cytoarchitectural atypia. It is benign/borderline or malignant according to the degree of dysplasia ± invasion (20-30% are associated with colloid or ductal adenocarcinoma). 80% are in the head of pancreas and multifocal within the duct system. It shows indolent behaviour marked by MUC 2 phenotype in distinction from the MUC 1 aggressive ductal phenotype of usual pancreatic cancer.

— serous macro/microcystic tumours:

elderly in the head or tail (50-75%) and mostly benign (micro-cystic/oligocystic serous adenoma) but occasionally malignant. It comprises glycogen-rich, clear cuboidal epithelium lining fluid-filled microcysts with a central scar. Diagnosis can be aided by analysis of aspirated cyst fluid which, in distinction from mucinous cystic tumours and pseudocysts, has low viscosity and zero levels of leucocyte esterase. Surgical excision is curative.

— mucinous cystic tumours:

benign/borderline/malignant spectrum of appearance and behaviour tending to malignancy. Prognosis relates to the degree of invasion (which can be focal within a lesion) into pancreatic and extrapancre-atic tissues. The carcinoma is usually ductal in character, occasionally adenosquamous or pleomorphic/giant cell. In general, indolent growth with spread to abdominal cavity occurring in middle-aged women but 90-95% 5-year survival if completely excised. Uni-/multi-locular, body/tail of pancreas and potentially resectable. Characteristic ovarian type stroma in the wall (helpful to distinguish from pancreatic pseudocyst when the epithelial lining is lost) and no connection to the duct system.

— solid-cystic-papillary tumour (syn. solid-pseudopapillary tumour):

adolescent girls/young women of low malignant potential but usually benign. It comprises pseudopapillae covered by several layers of uniform, endocrine-like epithelial cells and a vascularized, hyali-nized stroma with necrosis and mucinous cystic change. Alpha-1-antitrypsin/vimentin/CD 10 positive, ± neuroendocrine markers (chromogranin/CD56/synaptophysin), and cytokeratin negative.

— acinar cell carcinoma:

1-2% of cases in the head of pancreas and uniform cells with cytoplasmic granules resembling normal pancreas. Enzyme antibody positive, e.g. lipase, amylase, trypsin. Nodal and liver metastases can be present in 50% of cases at diagnosis and aggressive.

— mixed differentiation carcinoma:

acinar/endocrine or ductal/endocrine are rare and behave as for ductal carcinoma. The endocrine component must be at least 30 % of the tumour.

— small cell carcinoma:

presents at late stage, poor prognosis.

— pancreaticoblastoma:

malignant in children and favourable prognosis if resected before metastases (nodal/hepatic 35% of cases). Also chemoresponsive. Consists of epithelial (acini, squamous nests) and mesenchymal (spindle cell) components.

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