Moreover, chronic stress elevates IL-6 production in rheumatoid arthritis (RA), reducing anti-inflammatory effects of glucocorticoids in RA patients (Davis et al., 2008), and promotes breast cancer metastasis by accumulating myeloid-derived suppressor cells via the activation of β-adrenergic signaling and the IL-6/STAT3 pathway (An et al., 2021). Here, STAT3 is linked to breast cancer.