Abstract: Purpose :To evaluate the probability of using chromosome aberrations induced by irradiation as a indicator of future cancer risk. Methods :Chromosome aberrations in peripheral blood lymphocytes of 10 irradiated and 6 nonirradiated nasopharyngeal carcinoma patient s were studied by two - colour fluorescence in situ hybridization (FISH) and coventional analysis. Results :Both the mean t ranslocation and dicent ric f requencies in irradiated patient s 1 to 10 years after exposure were still significantly higher than those in nonirradiated patientP < 0. 001) . For irradiated patients ,the translocation f requencies were about 3. 5 - fold as high as dicent ric f requencies. No significant difference was found between t ranslocation f requencies in patient s after exposure more than 3 years and that in patient s after exposure less than 3 years ( P > 0. 1) ,but the dicent ric f requencies in patient s after exposure more than 3 years were significantly lower than that in patient s after exposure less than years( P < 0. 001) Conclusion :The percentages of stable chromosome aberrations ( translocations) are still higher even a long time (10 years) after exposure and is expected to be a re1evant biomarker of future cancer risk.

Key words: FISH, radiotherapy, chromosome aberration