Ironing out a survival strategy Metastatic cells display a notable ability to adapt to—and even thrive in—harsh microenvironments. One extreme example is leptomeningeal metastases (LM), cancer cells that enter a region of the central nervous system called the subarachnoid space, which is filled with cerebral spinal fluid (CSF). This anatomic site has a limited supply of micronutrients such as iron, and it harbors immune cells. Chi et al. used single-cell RNA sequencing to study CSF samples from cancer patients with LM (see the Perspective by Garzia and Taylor). They found that LM cells express and use components of a high-affinity iron-capturing system. Through this mechanism, the LM cells avoid the adverse effects of iron deprivation and potentially escape immune attack by limiting the supply of iron to macrophages. Science this issue p. 276 ; see also p. 250