The Niche Awakens: Comprehension of Cancer Stem Cells’ Microenvironment to Plan New Therapeutic Strategies

Cancer stem cells (CSCs) are a highly influential population of tumor cells involved in tumor initiation, progression, metastasis, recurrence, and resistance to therapy. Although CSCs have been widely investigated, their behavior cannot be understood solely through intrinsic cellular features, as these cells strongly depend on a specialized supportive microenvironment known as the CSC niche. In this review, we discuss the CSC niche as a dynamic and therapeutically relevant ecosystem that is distinct from, but closely connected with, the broader tumor microenvironment. Particular attention is given to stromal cells, immune cells, endothelial cells, extracellular matrix components, hypoxia, cytokines, chemokines, and metabolic stress as regulators of CSC self-renewal, plasticity, dormancy, immune escape, epithelial–mesenchymal transition, metastatic dissemination, and survival under therapeutic pressure. We further consider how CSC–niche interactions contribute to pre-metastatic niche formation and tumor relapse. Finally, we outline emerging therapeutic strategies aimed at disrupting CSC-supportive signals, including approaches targeting developmental pathways, angiogenesis, hypoxia, extracellular matrix remodeling, immunosuppressive networks, and cytokine-mediated communication. Overall, this review emphasizes that targeting the CSC-supportive microenvironment is essential for limiting metastasis, recurrence, and long-term treatment failure.