FOS and neoplasm: In addition, RANK/RANKL activation triggers intracellular signaling pathways (e.g., MAPK, NF-kB, Fos/AP-1, JNK/ERK/P38), which are involved in tumor proliferation and metabolic activities (42).There are many preclinical studies on the above-mentioned signaling pathways in RANKL activation-induced cancer metastasis.