Cancer metastasis remains the principal driver of cancer mortality worldwide. Despite significant progress in targeted therapies and immunotherapies, the ability of tumors to spread to distant organs continues to challenge clinicians and researchers alike. Understanding why some cancer cells evade immune surveillance, survive in hostile microenvironments, and colonize new tissues requires experimental systems that reflect the complex physiology of human tumors. Increasingly, researchers are turning to human-relevant models—3D cultures, organoids, and organ-on-chip platforms—to bridge the gap between conventional laboratory studies and patient outcomes. These systems enable studies under conditions that approximate the spatial, metabolic, and immunological gradients present in real tumors, offering critical insight into metastasis biology.