The aim of this investigation was to study the peculiarities of the cancer of the mammary gland depending on its histogenesis, histological form, character of growth, degree of malignancy and stages of development on the postop-erational material. As a research material 72 cases of the cancer of the mammary gland have served. The level of the expression of marker CD 31 depending on the degree, zone and form of the cancer of the mammary gland was studied by immunohystochemical method. The results of the research have shown that the peripheric zone of the cancer intensively supplied by the vessels of type of capillaries, in comparison with the central zone there is not many gigantic capillaries of type of sinusoids surrounded with tumoral cells, but is a lot of cells marked an angiogenesis marker - CD 31. Number of marker CD 31 in the cancer tissue changes depending on degree of differentiation of the tumoral tissue, it increases according to degree of malignancy of cancer. For example, monoclon CD 31 in the tumoral cells more intensively in medullary forms of the cancer than in tubular forms