Although miR-155 is frequently described as an oncogenic microRNA in prostate cancer, increasing evidence indicates that miR-155-5p may also exert tumor-suppressive functions under specific conditions, particularly through the negative regulation of metastatic and inflammatory signaling pathways such as TGF-β/SMAD2, NF-κB, and SPOCK1. The gene discussed is SMAD2; the disease is Familial prostate cancer.