Fine structure of three major grades of malignancy of human pancreatic adenocarcinoma

Fine structural analysis of a series of 51 adenocarcinoma in the human pancreas revealed their composition of one major cell type, a mucoprotein secreting cell which has a number of structural features resembling the cells of the larger interlobular ducts in the normal pancreas. In addition to mucus secretion, the tumor cells released large quantities of membrane material, both as vesicles pinched off from microvilli and as blebs sequestered from the plasma membrane. At the ultrastructural level the subdivision of tumors into three major grades of malignancy was manifested by a progressive loss in cell polarity and a reduction in the association of tumor cells with elements of the extracellular matrix (basal lamina). The highest grade of differentiation grew as tubular structures with a common luminal space, while with progressive dedifferentiation and loss of cell polarity secretion occurred into both luminal and interstitial spaces. This release pattern of tumor cell products, which constitute a complex mixture of exportable and constitutive proteins, will lead to their appearance in both pancreatic juice and blood circulation. Tumor cell spreading occurred along perineural sheaths and was combined with nerve fiber destruction. Primary tumors and lymph node or liver metastases did not differ significantly in their respective grading.