Relationship between size and oxygenation status of malignant tumors.

Analyzing the oxygenation status of tumors by means of the oxyhemoglobin saturation of single red blood cells within microvessels, there is clear evidence that tissue hypoxia and anoxia are inherent features during advanced stages of malignant growth. This is a consequence of distinct deteriorations of the convective and diffusive O2 transport with increasing tumor size leading to an O2 depletion in peripheral tissue layers around nutritive blood vessels. These alterations are combined with inhomogeneities of the oxygen distribution, both spatial and temporal. With enlarging tumor mass, the heterogeneities of the O2 supply distinctly intensify. Although in vitro experiments utilizing multicell spheroids failed to show very low oxygen tensions in necrotic regions, it is still proposed that chronic oxygen depletion is a paramount factor for the induction of necrosis in solid tumors under "physiological" in situ conditions.