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Growing evidence suggests that somatic hypermutational status and programmed cell death-1 overexpression are potential predictive biomarkers indicating treatment benefits from immunotherapy using immune checkpoint inhibitors.However,biomarker-matched trials are still limited,and many of the genomic alterations remain difficult to target.To isolate the potential somatic hypermutational tumor from microsatellite instability low/microsatellite stability (MSI-L/MSS) cases,we employed two commercial kits to determine MSI and forensic short tandem repeat (STR) alteations in 250 gastrointestinal (GI) tumors.Three types of forensic STR alteations,namely,allelic loss,Aadd,and Anew,were identified.62.4％ (156/250) of the patients with GI exhibited STR alteation,including 100％ (15/15) and 60％ (141/235) of the microsatellite high instability and MSI-L/MSS cases,respectively.30％ (75/250) of the patients exhibited STR instability with more than 26.32％ (26.32％-84.21％) STR alteation.The cutoff with 26.32％ of the STR alteations covered all 15 MSI cases and suggested that it might be a potential threshold.Given the similar mechanism of the mutations of MSI and forensic STR,the widely used forensic identifier STR kit might provide potential usage for identifying hypermutational status in GI cancers.