PRL and major depressive disorder: In the present study, MMP-9 was found to exhibit “metalloendopeptidase activity.” In addition, KEGG analysis revealed that the common DEGs were enriched in 28 pathways including “transcriptional misregulation in cancer,” “metabolic pathways,” “endometrial cancer,” “prolactin signaling pathway,” and “MAPK signaling pathway.” Prolactin was observed to promote bone metastasis in breast cancer patients, possibly by stimulating lytic osteoclast formation [28], and data from an animal model of MDD also supported the pathological role of prolactin in MDD [29].