Mounting evidence shows that long noncoding RNAs play important roles in human diseases and radioresistance could be an important factor for tumor recurrence. We observed that HOX antisense intergenic RNA () expression increased in invasive ductal carcinoma (IDC) tissue. The irradiation effect of was detected by 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS) assay, cell cycle and apoptosis analysis, and xenografts in nude mice. Western blot, RNA pulldown assay, and RNA immunoprecipitation were used for mechanistic studies. , upregulated in IDC of breast cancer tissue, could promote breast cancer cell proliferation by regulating cell cycle and apoptosis. Overexpression of promoted DNA damage repair factors KU70, KU80, DNA-PKs, and ATM expression, and these could be impeded by small molecular inhibitors of enhancer of zeste homolog 2 (). Meanwhile, we found that could facilitate recruitment of to the Avian Myelocytomatosis Viral Oncogene Homolog (MYC) promoter. is an important modulator not only to the prognostic of breast cancer, but also a good marker for radiotherapy.