PTHLH and cancer: Metastatic cancer cells produce special enzymes, such as matrix metalloproteases (MMPs), cytokines (IL-6, IL-8, IL-11), parathyroid hormone-related protein (PTHrP), chemokine receptor (CXCR4), osteopontin (OPN), and bone sialoprotein (BSP) which help to invade bone marrow (18–24).