DKK1 and bone metastasis: Predictive value of serum DKK1 in the subgroups of bone metastases, such as in those with solitary bone metastasis, multiple bone metastasis, isolated bone metastases, additional visceral or cerebral metastases, stage N0 + N1, stage N2 + N3, stage T1 + T2 and stage T3 + T4 were further investigated.