CTSK and neoplasm: Furthermore, quantitative polymerase chain reaction (qPCR) analyses corroborated the downregulation of key osteoclast-associated genes, including Ctsk, c-Fos, Nfatc1, Mmp9, and Atp6v0d2 in bone marrow of the tumor-bearing limbs, as well as upstream regulators, Rankl and Pthrp, in tumors (Fig. 4O), which are critical in initiating osteoclast differentiation.