Although a previous study on bone metastasis of prostate cancer also showed that GDF15 in osteocytes promoted EGR1 expression in prostate cancer cells and that enhanced EGR1 promoted the growth and invasive of prostate cancer cells [46], there are no previous reports of a GDF15–EGR1 positive feedback loop in tumor progression. The gene discussed is GDF15; the disease is prostate carcinoma.