The frequency of chromosomal translocations was analyzed in skin fibroblast cell cultures derived from irradiated and nonirradiated skin biopsies from five cases of breast adenocarcinoma in women, who had undergone radiotherapy after surgery. The study was performed at the first annual check-up. Chromosomal in situ suppression (CISS) hybridization was performed using metaphase nonisotopic fluorescence in situ hybridization (FISH) with library probes specific for chromosomes 1, 2, 3, 4, 5, 7, 8, 13, 19, and 20. The results showed that the frequency of clonal translocations in metaphases obtained from irradiated areas was significantly higher than in metaphases from the nonirradiated tissue samples.Facultad de Ciencias Naturales y Museo