Abstract: Objective To study genetic alterations in 13 CODIS STR loci in various tumor tissue samples from human digestive system. Methods Malignant tumor tissues and blood samples taken from 55 different unrelated individuals were collected. DNA samples were extracted using Chelex100 extraction kit, amplified using Profiler and Cofiler PCR amplification kit and analyzed using API 310 analyzer. Results Aberrant cell divisions were detected in all of the 55 tumor tissue samples, with STR alternations detected in two samples including allelic alteration, partial and complete loss or unbalance of heterozygosity. Moreover, the alternations might occur simultaneously at more than one loci. Conclusion Caution must be taken in STR analysis of tumor tissue samples since the exclusion loci in forensic identification or paternity testing may be resulted from mutations in the tumor tissue.

Key words: STR loci, allelic alternation, tumor tissue, human digestive system