Measurement of the hypoxic cell fraction in human tumors using a comet assay

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Purpose : The prediction of tumor radiosensitivity is very important in radiation therapy for malignant diseases. We have developed our own method and image analysis system for a comet assay to identify hypoxic fractions. We tested our system using a cultured tumor cell line, and compared the hypoxic cell fractions in murine tumors detected by this assay with those determined by a radiobiological assay. In this study, we further confirmed whether the comet assay is clinically useful for estimating hypoxic fractions of solid tumors. Material and Methods : Under permission of the Internal Review Board, 17 patients (5 with uterine cervical cancers, 6 with pancreatic cancers and 6 with osteosarcomas) were enrolled in this study. Patients with uterine cervical cancers were treated with external beam irradiation and intracavital irradiation, and other patients were treated with intraoperative irradiation. Just after the intracavital or intraoperative irradiation, we obtained a small sample from the tumors and analysed the hypoxic cell fraction using the comet-assay. Results : From 9 of 16 tumors, we could obtain sufficient cells to perform the comet-assay. Although it was possible to determine the hypoxic cell fraction clearly in the in vitro and in vivo experiments, it was very difficult to detect hypoxic cell fraction in the clinical material. Therefore, we only identified radioresistant cell fractions in this study. These fractions comprised between 4.2 and 21%. We will compare these results with clinical outcomes in the future. ;