Ferroptosis has emerged over the past decade as a compelling therapeutic avenue for cancer, prompting intense interest in strategies that selectively induce or inhibit this form of cell death. Although substantial progress has been made in identifying genes that regulate ferroptosis sensitivity and in developing small-molecule modulators, it remains unclear which molecular targets offer the greatest therapeutic potential in specific tissues and contexts. Here, we highlight fundamental differences between in vitro and in vivo ferroptosis modulation, with emphasis on the integration of different techniques, mouse models, and how the tumor microenvironment shapes two major ferroptosis surveillance pathways: glutathione peroxidase 4 and ferroptosis suppressor protein 1. We propose that integrating in vivo biological constraints and microenvironmental complexity is essential for the rational design and successful translation of ferroptosis-targeted therapies.