TNFRSF11A and depressive disorder: The links encompassing severe depression, high sympathetic tone, increased RANKL expression in bone, and higher incidence of bone metastasis reported in our study, as well as the poor prognosis of breast cancer patients with high tumor RANK expression [41], provide an explanation for the observed correlation between emotional stress and reduced survival of patients with breast cancers [42]–[44], which will obviously have to be confirmed by further clinical or epidemiological studies.