76 cases of gastric cancer (26 of intestinal type, 35 of diffuse and 15 of mixed type) served as the material of the study. On this basis the relationship of tissue, cellular and functional differentiation of gastric cancer was studied. Its severity was compared to proliferative activity of tumor cells and invasion of blood vessels. Primarily, all types of gastric carcinomas were distinguished by the severity of differentiation at the tissue level. For example, gastric cancer of intestinal type was characterized by high and moderate tissue differentiation (26 cases - 100%), gastric cancer of diffuse type - by low tissue differentiation (35 - 100%), mixed type of gastric cancer occupied an intermediate position. On the contrary, differentiation of tumor cells was mostly low and moderate in intestinal type of gastric carcinoma (17 cases - 65.38%) and high (27 observations - 77.14%) in diffuse type (p <0.05). Intestinal type was characterized by low and moderate functional differentiation, mixed gastric cancer - by moderate, whereas the diffuse type of gastric cancer was characterized by moderate to high functional differentiation (32 cases - 91.43%). Various lines of functional differentiation (production of neutral and / or acid mucin, the presence of neuroendocrine granules, loss of expression of cytokeratins, expression of mesenchymal marker vimentin) were often detected in its cells, that is associated with the development of epithelial- mesenchymal transition, as an extreme degree of dedifferentiation.The differences of incidence and spread of epithelial-mesenchymal transition in the different histological types of gastric carcinoma were detected. Focal epithelial-mesenchymal transformation dominated in the intestinal and mixed types (16 - 61.53%, and 13 cases - 86.66%, respectively). Diffuse type of gastric carcinoma is characterized by spread epithelial-mesenchymal transition (30 cases - 85.71%) (p <0.05). Epithelial-mesenchymal transformation was detected in 18 cases of intestinal type of gastric carcinoma (invasion was in 12 (66.66%) of them) and in 14 cases of mixed type (vascular invasion was detected in 11 (78.57%)). The invasiveness of the diffuse type of gastric cancer was the highest (80.0% - 28 cases), with the presence of epithelial-mesenchymal transformation in all 35 observations of this type. The presence of epithelial-mesenchymal transformation in gastric carcinomas significantly influenced the increase of invasive potential of tumor (p <0.05). The processes occurring in the dynamics of epithelial-mesenchymal transformation are not compatible with cell division, so in the intestinal and mixed type of gastric cancer reduction of tumor proliferative activity was observed in the foci of transformation on the edge of invasion, while for the rest of the tumor proliferation was high. Low proliferative activity of tumor cells throughout the tumor dominated in almost all cases of the diffuse type of gastric cancer. Thus, the presence of epithelial-mesenchymal transition in gastric carcinoma, as an extreme degree of cell, tissue and functional dedifferentiation of the tumor, determines biological behavior and prognosis of the tumor. This information is necessary to define the aggressiveness of treatment of gastric cancer for each patient.
