Relation between Ku80 and microRNA-99a expression and late rectal bleeding after radiotherapy for prostate cancer.

Background and Purpose: Late rectal bleeding is one of the severe adverse events after radiotherapy for prostate cancer. New biomarkers are needed to allow a personalized treatment.
Materials and Methods: Four patients each with grade 0-1 or grade 2-3 rectal bleeding were randomly selected for miRNA array to examine miRNA expression in peripheral blood lymphocytes (PBLs). Based on results of miRNA array, 1 of 348 miRNAs was selected for microRNA assays. Then, expression of DNA-dependent protein kinase mRNA and miR-99a was analyzed in the PBLs of 97 patients. PBLs were exposed to 4Gy of X-ray ex-vivo.
Results: In the discovery cohort, grade 2-3 rectal bleeding was significantly higher in the Ku80 <1.09 expression group compared with ⩾1.09 group (P=0.011). In radiation-induced expression of miR-99a, grade 2-3 rectal bleeding was significantly higher in the miR-99a IR(+)/IR(-) >0.93 group compared with ⩽0.93 group (P=0.013). Most patients with grade 2-3 rectal bleeding were in the group with low Ku80 and high miR-99a expression. In the validation cohort, similar results were obtained.
Conclusion: A combination of low Ku80 expression and highly-induced miR-99a expression could be a promising marker for predicting rectal bleeding after radiotherapy.
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