A novel molecular mechanism involved in progression and metastasis in the most aggressive form of breast cancer has now been identified by researchers. The gene MAFK is known to be induced by the TGF-? signaling pathway, which is involved in breast cancer development. The team reported that MAFK protein, in turn, induced cancerous behaviors in cells by switching on the breast cancer-associated gene GPNMB. MAFK thus represents a link between TGF-? signaling and GPNMB-induced breast cancer.