piR-DQ598677, which is down-regulated in BC, inhibits BC growth post-transcriptionally through piRNA-RNA imperfect base-pairing-mediated RNA degradation as it is complementary to the 5′-UTR, 3′-UTR, and coding region of TAX1BP, TNFESF10B, and SFRP2 mRNA, respectively, which are involved in key cancer cell functions such as cell-to-cell signaling and interaction, cell death and survival, and cell cycle [47]. This evidence concerns the gene SFRP2 and breast cancer.