[Intratumoral proliferation of the blood vessels]

The growth of vessels in experimental neoplasm occurs within 2-7 days after implantation. Newly formed vessels penetrate into the tumor only from the tissues of the tumor-carrying host. Vessels are formed in the tumor by budding. Proliferation of tumor cells begins only after the contact between them and the developing vascular network has been established. Myofibroblasts play an important role in the development of vessels. The intensity of new vessel formation is more than twice as high as in the wound process. The number of capillaries in developed tumors varies with an average of 30,000 in 1 mm2. Blood supply even within the same tumor is variable both in the form and location of the vessels. With increasing tumor volume intercapillary distances, diameter and length of the capillaries increase while the vascular bed volume, the general and local blood flow decrease. Reparation of the vascular bed in tumors occurs both due to preexisting vessels and by additional formation of new vessels. The muscular layer and innervation are lacking in the newly formed vessels. In the process of growth, compensatory-adaptative reactions directed to improvement of hemodynamics constantly develop in tumor tissues.