TNFSF11 and neoplasm: For example, mice lacking soluble RANKL (Tnfsf11 ΔS/ΔS) have normal bone homeostasis and develop a normal immune system, but they display a marked reduced formation of bone metastases after inoculation of RANK-expressing melanoma or breast cancer cells, indicating that bone-derived soluble RANKL attract RANK-expressing tumor cells in the bone marrow [36].