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RESEARCH PRODUCT

Effect of Cell Line and Differentiation on the Oxygenation Status of Experimental Sarcomas

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Since the measurement of tumor oxygenation status and the fraction of hypoxia within tumor tissue by computerized pO2-histography [10] has become increasingly im-portant in the clinical setting, many studies on tumor oxygenation in different experimental malignancies as well as in various human tumors have been carried out. Because pO2-histography is an invasive technique, this method has been used in humans mostly in superficial primary tumors and lymph node metastases [1,3,10] (for a review see [9]). Experimental studies in animals have been carried out on a wide range of isotransplanted rodent sarcomas or carcinomas [2,4,6–8,11] and of xenotransplanted human tumors [6]. The results obtained have however been quite variable, often producing conflicting data which are difficult to interpret, presumably due to the use of a variety of tumor entities, sites of tumor growth, and differentially differentiated tumor cells. However, if therapeutic modulation of the tumor oxygenation is the aim of an experimental study, the pre-treatment oxygenation status is an important factor influencing the experimental results. If, for instance, a study is carried out on the modulatory effect of respiratory hyperoxia on the ra- diosensitivity of a tumor, the beneficial effect of O2 breathing depends on the initial tumor pO2. Since radiosensitivity of tissues is half-maximal at a pO2 of 3–4 mmHg, the effect of sparsely ionizing radiation cannot be improved when hypoxia is not present in the tumor. This fact might explain the varying results on the therapeutic effect of oxygenation modulators on radiosensitivity of solid tumors.