Introduction:
The present study aimed to explore the effects of pri-let-7a-1 rs10739971 and FAS-670 rs1800682 polymorphisms on the pathogenesis of radiation induced intestinal toxicity in prostate cancer (PC) patients.

Material and methods:
380 PC patients with or without signs of intestinal toxicity were enrolled to study the effects of let-7a rs10739971 and FAS-670 rs1800682 polymorphisms on rectal volume and the risk of intestinal toxicity. In addition, real-time PCR, Western-blot analysis, immunohistochemistry, luciferase assays and computational analyses were performed to explore the mechanism underlying the role of let-7a rs10739971 polymorphism in radiation induced intestinal toxicity.

Results:
The let-7a rs10739971 polymorphism but not the FAS-670 rs1800682 polymorphism was closely related to the risk of radiation induced intestinal toxicity featured by a high rectal volume. In addition, there was no obvious association between the rectal volume and the genotype and allele frequencies of FAS -670 rs1800682 and Pri-let-7a-1 rs10739971 polymorphisms. The GG genotype of let-7a rs10739971 polymorphism reduced let-7a expression but enhanced FAS expression. In addition, the intestinal toxicity (-) group showed a much higher level of let-7a and a much lower level of FAS than the intestinal toxicity (+) group. FAS was a virtual target gene of let-7a, which decreased FAS protein expression in a dose-dependent manner.

Conclusions:
The GG genotype of pri-let-7a-1 rs10739971 polymorphism could increase the risk of radiation induced intestinal toxicity in PC patients. Therefore, the pri-let-7a-1 rs10739971 polymorphism could be used as a putative marker to predict the risk of intestinal toxicity in PC patients undergoing radiotherapy.