A novel cDNA encoding a secreted form of osteoclast differentiation factor/tumor necrosis factor-related activation-induced cytokine (sODF/TRANCE, GenBank Accession No. AB037599) was sequenced from 5' RACE cDNA clones of squamous cell carcinoma cell lines, SCC-4 and T3M-1 Cl.2, of which parental malignant tis;sues had caused severe humoral hypercalcemia The sODF/TRANCE cDNA was composed of unknown 5' end sequence followed by the 100% identical sequence of the ODF/TRANCE extracellular domain-coding region. The longest open reading frame (ORF) of the novel cDNA completely matched the 3' end of the ORF of the ODF/TRANCE cDNA encoding C-terminal amino acid residues (74-318) in the extracellular region. The corresponding protein that reacted with the antibody specific for the extracellular domain of ODF/TRANCE was detected in the culture media conditioned by the cancer cells. Furthermore, human promyeloblastic leukemia cells HL60, differentiated into osteoclast-like cells (OCLs) when cultured in the media conditioned by SCC-4 and T3M-1 CL2 cells. The differentiation of HL6O cells into OCLs was inhibited by the anti-ODF/TRANCE antibody. These results strongly suggest that sODF/TRANCE plays an important role in enhanced bone-resorption in humoral hgpercalcemia of malignancy