IL6 and breast cancer: In breast cancer, bone marrow cells secrete parathyroid hormone-related protein (PTHRP), TNF-α, interleukin 6 (IL-6), and/or IL-11 stimulate the release of the receptor activator of NF-κB ligand (RANKL) from osteoblasts and suppress the release of the RANKL antagonist osteoprotegerin, allowing for breast tumor CTCs to colonize the bone marrow (37).