Divergent iron-regulatory states contribute to heterogeneity in breast cancer aggressiveness.

Similar primary tumors can progress to vastly different outcomes, where transcriptional state rather than mutational profile predicts prognosis. A key challenge is to understand how such programs are induced and maintained to enable metastasis. In breast cancer cells, aggressive transcriptional signatures and migratory behaviors linked to poor patient prognosis can emerge as a result of contact with a collagen-rich microenvironment mimicking tumor stroma. Here, we leverage heterogeneity in this response to identify the programs that sustain invasive behaviors. Invasive responders are characterized by expression of specific iron uptake and utilization machinery, anapleurotic TCA cycle genes, actin polymerization promoters, and Rho GTPase activity and contractility regulators. Non-invasive responders are defined by actin and iron sequestration modules along with glycolysis gene expression. These two programs are evident in patient tumors and predict divergent outcomes, largely on the basis of ACO1. A signaling model predicts interventions and their dependence on iron availability. Mechanistically, invasiveness is initiated by transient HO-1 expression that increases intracellular iron, mediating MRCK-dependent cytoskeletal activity and increasing reliance on mitochondrial ATP production rather than glycolysis.