We, therefore, focused on the investigation of correlations among microRNA-378a-3p (miR-378), which inhibits the progression of prostate cancer (PCa) through the suppression of kallikrein-related peptidase (KLK) genes, such as KLK2, KLK4, KLK6, and KLK14, and how EPA drives the expression level of miR-378 in cancer cells. The gene discussed is KLK4; the disease is prostate carcinoma.