Breast cancer (BC) is the most common cancer among women and the most common cause of women`s death from cancer both worldwide and in Egypt. It is a complex disease that results from interaction between genetic susceptibility and environmental risk factors. Approximately 5-10% of all breast cancer cases are caused by genetic mutations, the majority of which can be accounted for (BRCA1) and (BRCA2) but other genes are also involved. PIWI-interacting RNAs (piRNAs) is a class of small non-coding RNAs. Normally piRNAs are involved in the silencing of genetic elements, including transposable elements (TEs). They also play a role in regulation of gene expression. The disruption of piRNAs that normally suppress TE activity may facilitate genomic instability, thereby contributing to tumorigenesis. Aberrant expression of a number of piRNAs has been identified in many cancers. The Pi-RNA 021285 SNP (rs1326306) is a polymorphism in which a guanine nucleotide (G) is substituted with a thymidine (T) nucleotide at base 12 of piR-021285 which results in increased expression of ARHGAP11A gene. ARHGAP11A gene is a protein coding gene located on the long arm of chromosome 15, it is an oncogene that regulates proliferation, invasion and metastases of tumor cells. It is overexpressed in a variety of tumors as colon cancer, brain, lung cancers and breast cancer.