Tumor Microenvironment: The Kingpin in the Emergence of Resistance to Cancer Therapy

The landscape of cancer biology has undergone a profound transformation over the past two decades. Historically, cancer was largely viewed as a disease driven by intrinsic genetic mutations within malignant cells, and therapeutic strategies were primarily designed to target these aberrant molecular pathways. However, accumulating evidence has fundamentally reshaped this perspective by demonstrating that tumor behavior cannot be fully understood by studying malignant cells in isolation. Instead, tumor development, progression, immune escape, and therapeutic response are profoundly influenced by the surrounding tumor-microenvironment (TME). This evolving understanding has shifted oncology from a tumor-centric discipline toward one that recognizes cancer as a dynamic and adaptive ecosystem.

The TME is an extremely heterogeneous and dynamic environment composed of diverse cellular and non-cellular elements. These include endothelial cells that form vascular networks; immune cells such as macrophages, lymphocytes, and dendritic cells; cancer-associated fibroblasts; extracellular matrix components; and a wide range of cytokines, chemokines, and growth factors. These components engage in continuous bidirectional communication with tumor cells and collectively influence proliferation, angiogenesis, metastatic dissemination, metabolic adaptation, and immune regulation. Importantly, the TME is not merely a passive scaffold for tumor growth; rather, it actively determines whether tumors remain susceptible or become resistant to therapy.

One of the central themes emerging from the studies included in this Special Collection is that therapeutic resistance rarely arises from tumor-cell intrinsic mechanisms alone. Instead, resistance evolves through coordinated interactions between malignant cells and the surrounding stromal and immune compartments. Across diverse tumor settings, the collected studies converge on the idea that the TME establishes a protective niche that dampens antitumor immunity, promotes cellular plasticity, and facilitates adaptation to therapeutic stress. Although contemporary cancer therapies have achieved substantial advances, particularly in immunotherapy and targeted therapy, durable clinical responses remain limited for many patients. The studies presented here collectively raise an important unresolved question: why do therapies directed primarily against tumor cells often fail to achieve sustained control when the supportive microenvironment remains largely intact? By highlighting these emerging concepts, this Special Collection aims to underscore the importance of integrating microenvironment-targeted strategies into future therapeutic paradigms. A deeper understanding of the complex crosstalk between tumor cells and their microenvironment will be essential for the development of more effective, durable, and personalized approaches to cancer treatment.

A recurring concept highlighted throughout the collection is the close interplay between cancer stem cells (CSCs) and the TME. CSCs represent a highly resilient tumor cell subset capable of self-renewal, metastatic dissemination, and tumor re-initiation following treatment. However, the studies collectively demonstrate that CSC survival is critically dependent on signals derived from the surrounding microenvironment. Interactions with stromal cells, immune populations, inflammatory mediators, and ECM components collectively establish specialized niches that preserve stemness and shield CSCs from immune-mediated elimination and therapeutic injury. Chakraborty et al further emphasize that CSC–TME crosstalk contributes to the establishment of profoundly immunosuppressive conditions that limit the effectiveness of immune checkpoint inhibitors and adoptive cell therapies. ¹ Together, these observations underscore a broader challenge in oncology: therapeutic strategies directed solely at eliminating proliferating tumor cells may be insufficient unless the microenvironmental programs sustaining CSC persistence are simultaneously disrupted.

Another major aspect connecting the contributions in this collection is the role of inflammatory signaling pathways in shaping therapeutic outcomes. Rather than acting as isolated molecular events, inflammatory pathways function as integrative networks that coordinate communication between tumor cells and the surrounding microenvironment. Among these, nuclear factor kappa-B (NFκB) signaling has emerged as a critical molecular regulator that connects inflammation to the growth of tumors and resistance to treatment. NFκB serves as a central hub in the tumor-microenvironment, integrating signals from growth factors, cytokines, and stress-related stimuli to influence surrounding stromal and immune populations as well as tumor cells. Mukherjee et al describe the context-dependent nature of NFκB activation within the TME, highlighting its paradoxical capacity to support both immune activation and tumor-promoting inflammation. ² Acute or tightly regulated NFκB signaling may facilitate immune surveillance and antitumor responses by facilitating the expression of inflammatory mediators that support immune cell recruitment and activation, whereas sustained activation often drives chronic inflammation, angiogenesis, immune suppression, and enhanced tumor survival. Importantly, these studies collectively illustrate that therapeutic inhibition of inflammatory pathways remains challenging because broad suppression of inflammation may also compromise beneficial antitumor immunity. This unresolved therapeutic dilemma continues to represent a major obstacle in translating mechanistic insights into durable clinical benefit.

The collection also reinforces the importance of immune-cell plasticity within the TME, particularly the role of tumor-associated macrophages (TAMs). Macrophages demonstrate remarkable phenotypic adaptability in response to local environmental cues, ranging from pro-inflammatory antitumor states (M1 phenotypes) to immunosuppressive tumor-supportive (M2 phenotypes. Across multiple cancer contexts, the tumor microenvironment selectively fosters the accumulation of M2-like macrophages that support angiogenesis, ECM remodeling, invasion, metastatic dissemination, and suppression of cytotoxic T-cell activity. Guo and Zhang discuss emerging strategies aimed at macrophage reprogramming as a means of restoring immune surveillance and enhancing therapeutic responsiveness. ³ Their work focuses on emerging therapeutic strategies that aimed at reprogramming macrophages into an anti-tumor phenotype, thereby restoring immune surveillance and improving the efficacy of cancer therapies. Importantly, the collective findings in this Special Collection suggest that effective immunotherapy may require not only activation of effector lymphocytes but also simultaneous remodeling of the immunosuppressive microenvironment that constrains their function.

This Special Collection contains studies that look at important clinical problems that come up during cancer treatment, as well as studies that look at how things work at the molecular and mechanistic levels. To turn what we know about tumor biology into better care for patients, we need to pay attention to both how tumors grow and how they become resistant to treatment, as well as the side effects of treatment that can make it less effective. In this context, Nakajima and colleagues present a clinical study assessing the efficacy of combining mirogabalin with duloxetine for the treatment of chemotherapy-induced peripheral neuropathy (CIPN) in patients receiving taxane-based chemotherapy for advanced lung cancer. ⁴ CIPN is mostly seen as an adverse effect of treatment rather than a direct microenvironmental phenomenon, but it has a big impact on patients. Severe neuropathy frequently requires dose reduction or cessation of chemotherapy, consequently diminishing therapeutic efficacy. The research indicates that mirogabalin may offer supplementary symptomatic relief in patients with refractory neuropathy when used in conjunction with duloxetine, potentially allowing patients to persist in anticancer therapy with enhanced tolerance and sustained treatment intensity.

Beyond mechanistic insights, the studies included in this issue also draw attention to clinically relevant barriers that indirectly contribute to treatment failure. To turn what we know about tumor biology into better care for patients, we need to pay attention to both how tumors grow and how they become resistant to treatment, as well as the side effects of treatment that can make it less effective. Nakajima et al evaluate the combination of mirogabalin and duloxetine for chemotherapy-induced peripheral neuropathy (CIPN) in patients receiving taxane-based therapy for advanced lung cancer. ⁴ Although CIPN is not traditionally categorized as a TME-driven process, this study highlights an equally important dimension of therapeutic resistance: treatment-associated toxicities frequently necessitate dose reduction, treatment interruption, or discontinuation, thereby limiting therapeutic intensity and compromising long-term disease control. Such observations broaden the discussion surrounding resistance by emphasizing that successful cancer therapy requires not only tumor eradication but also sustained treatment tolerability.

Collectively, the studies in this Special Collection emphasize that the TME operates as a dynamic regulator of tumor adaptation rather than a secondary bystander in cancer progression. They also highlight a persistent gap between mechanistic understanding and clinical translation. Despite major advances in immunotherapy, targeted therapy, and precision oncology, many therapeutic strategies still inadequately address the spatial and cellular complexity of the TME. Tumors continuously evolve through reciprocal interactions with immune, stromal, and metabolic networks, allowing them to escape therapeutic pressure through multiple parallel mechanisms. This complexity may partly explain why promising preclinical interventions often fail to generate durable responses in clinical trials.

The integration of emerging technologies, including spatial transcriptomics, single-cell sequencing, and multi-omics approaches, is now providing unprecedented insight into the heterogeneity and temporal evolution of the TME. These advances may help identify predictive biomarkers, context-specific therapeutic vulnerabilities, and rational combination strategies capable of overcoming resistance. However, the studies assembled in this collection collectively suggest that future therapeutic success will likely depend on simultaneously targeting malignant cells, immune suppression, stromal remodeling, inflammatory signaling, and CSC-supportive niches rather than addressing each component independently.

In conclusion, this Special Collection reinforces the concept that the tumor-microenvironment is a central orchestrator of cancer progression, immune evasion, and therapeutic resistance. Rather than presenting isolated mechanisms, the collected studies collectively illuminate the interconnected biological networks that sustain tumor persistence under therapeutic pressure. By bringing these themes together, the collection highlights both the promise and the current limitations of TME-directed therapies. A deeper mechanistic understanding of tumor–microenvironment interactions, coupled with clinically translatable strategies capable of remodeling this adaptive ecosystem, will be essential for achieving more durable and effective cancer control.