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The dependence of tumor growth on the development of new blood vessels was, for the first time, traced in vivo through a noninvasive procedure developed at the Institute and described in a recent issue of Cancer Research.
A major concept in solid tumor physiology states that tumors can grow only to a size of approximately 1 mm in the absence of new blood vessels, due to limited nutrient and oxygen supply. While supporting evidence for this hypothesis has been accumulating, the new study -- carried out by doctoral student Rinat Abramovitch, technician Gila Meir and Dr. Michal Neeman of the Institute's Department of Hormone Research -- furnishes quantitative documentation of this phenomenon.
Making use of noninvasive magnetic resonance imaging (MRI), the Weizmann team found a consistent four-day lag in the growth of tumors implanted in immune-deficient mice. During this period, blood vessels near the tumor began to develop. Rapid tumor growth was observed only after the fourth day following implantation, which was also when the new blood vessels reached the tumor.
"The ability to observe the early stages of new blood-vessel development in vivo in a tumor with well-defined initial conditions will open new possibilities for the evaluation of the role of metabolic stress in this critical stage of tumor establishment," the scientists write.
This study also demonstrated that tumor-induced generation of vessels could be measured separately from vessel formation triggered by wound healing. The separate measurements were made possible by positioning the tumor 1 cm away from the site of incision and simultaneously monitoring both tumor expansion and the wound-healing process.
Nearly all solid tumors evolved through two phases -- avascular (without vessels) and vascular. Cells of avascular tumors usually do not invade or violate the integrity of their host. In contrast, vascularized tumors appear to compress, invade and destroy neighboring tissue. This critical point of tumor vascularization may thus become a favorable target for various therapies.
Dr. Neeman is the incumbent of the Dr. Phil Gold Career Development Chair of Cancer Research.
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