For decades, cancer has been understood within a reductionist epistemology, as a sequence of genetic alterations that activate oncogenes, inactivate tumor suppressors, and drive uncontrolled proliferation (1). This model enabled key discoveries in molecular oncology but fails to explain emergent phenomena such as tumor heterogeneity, phenotypic plasticity, therapy resistance, and clonal evolution (2).

Hanahan’s 2022 update of the Hallmarks of Cancer expanded the original framework to include new enabling dimensions: non-mutational epigenetic reprogramming, polymorphic microbiomes, cellular senescence, and phenotypic plasticity (3). This conceptualization reframes cancer as a dynamic, evolving system in which biological capabilities emerge from multilevel interactions among genetic, epigenetic, and environmental components. Hanahan himself emphasizes that the hallmarks are heuristic tools for distilling the vast complexity of cancer phenotypes into a set of underlying organizational principles (3).

From this view, the tumor is not merely a mass of mutated cells but a complex adaptive system composed of interacting subsystems: epithelial, stromal, immune, and microbial elements that coevolve with their environment (4). Complexity theory, developed from systems physics, network theory, and ecology, privileges interactions over isolated entities, emergence over linear causality, and historicity over repetition (5). Applied to colorectal cancer, this framework positions the tumor as a dynamic ecosystem sustained by feedback loops, cooperation, and competition among its cellular and molecular components (6).

An integrative conceptual review was conducted to synthesize Hanahan’s 2022 hallmarks framework with literature on complex systems theory, tumor ecology, and colorectal carcinogenesis. The approach was explicitly non-systematic but analytically structured.

Relevant sources were identified through purposive searches in PubMed and Google Scholar, complemented by backward and forward citation tracking from seminal papers in cancer systems biology, complexity science, and colorectal cancer. Priority was given to: (i) highly cited conceptual and theoretical articles on cancer as a complex adaptive system; (ii) reviews and perspectives on tumor ecosystems, multiscale modeling, and systems oncology; and (iii) key empirical and translational works in colorectal cancer that illustrate emergent, network-level behaviors rather than isolated molecular events.

For the conceptual mapping, each hallmark and enabling characteristic was analyzed using predefined questions (1): Which interactions (cell–cell, cell–microenvironment, cell–microbiome) are necessary for this hallmark to manifest? (2) Which core properties of complex systems (nonlinearity, emergence, feedback, openness, interdependence, historical dependence) are required to sustain it? (3) How does the hallmark contribute to system-level adaptation or state transitions? Based on these criteria, hallmarks were iteratively assigned to one or more complexity properties, with emphasis on parsimony and internal coherence rather than exhaustive categorization. The objective was not to re-interpret primary molecular data but to construct a coherent systemic ontology of cancer grounded in established theoretical and experimental literature.

Colorectal cancer, when seen through the lens of complexity, ceases to be a sum of mutations and becomes an adaptive network governed by universal principles: emergence, feedback, self-organization, and openness. This paradigm explains heterogeneity and therapeutic resistance not as failures of precision medicine but as inevitable consequences of living systems capable of adaptation. It encourages the integration of multiscale models, agent-based simulations, and network approaches that incorporate molecular, ecological, and temporal data.

Understanding CRC as a complex system reframes therapy as ecological modulation rather than eradication. Targeting intercellular communication, metabolic cooperation, and microenvironmental dependencies may prove more effective than inhibiting single pathways. This shift aligns oncology with systems biology and network science, unifying the molecular and ecological dimensions of cancer.

This systems-oriented interpretation of colorectal cancer is consistent with advances in network biology, multiscale modeling, and ecological approaches to cancer, which conceptualize tumors as dynamic, interacting networks rather than linear molecular cascades (21–25). Recent work in cancer systems medicine and patient-specific mechanistic modeling further supports the integration of computational, ecological, and evolutionary frameworks to capture tumor behavior across scales (26–30).

Colorectal cancer should be conceived as a complex adaptive system where hallmarks emerge from collective organization rather than from discrete molecular events. The new dimensions proposed by Hanahan do not merely expand the list of hallmarks; they redefine cancer as an ecological, evolutionary, and self-organizing process. Embracing complexity offers not only a deeper theoretical understanding but also a pathway toward predictive and integrative oncology.