Ultrastructural comparative analysis of neuroendocrine tumors of pancreas

Abstract

Detection of ultrastructural distinctions of tumor cells and cell-to-cell cooperation in insulinomas and nonfunctioning neuroendocrine tumors of pancreas. Ultrastructural study of 38 insulinomas and 35 nonfunctioning neuroendocrine tumors of pancreas of the patients treated at Vishnevskiy Surgery Institute from 2010 to 2015. Insulinomas are characterized by high differentiation of intracellular organelles and specific secretory granules. In insulinomas the number of immature endocrine granules exceeded the number of mature granules. The tumor cells were often joined together and held with desmosomes ensuring very tight connection. Desmosome complexes were characterized by their extended length. Such ultrastructural changes were not followed by destruction of tumor cells. There was formation of specific syncytium-like structures consisting of cells connected by cytoplasmic channels with the common cytoplasm with cell organelles. In nonfunctioning tumors the most of the granules were distinguished by polymorphism and had no specific ultrastructure indicating the synthesized hormone. In large areas there were loss of plasmolemma integrity, up to its complete absence, which led to unification of cytoplasmic contents of the cells. Common junctions dominated in nonfunctioning tumors. Desmosomes were rare, poorly developed, and in the form of immature and reduced junctions. Complex cellular junctions are well developed in the cells, ensuring tight connection of tumor cells, reducing their invasive and metastatic potential. Nonfunctioning neuroendocrine tumors on the contrary are characterized by underdevelopment of cellular organelles and immaturity of secretory granules. Predominance of weak direct cell junctions, rupture of membranes of neighboring cells with simultaneous reduction of desmosomes facilitate the migration of individual tumor cells and formation of metastases.