Multidimensional tumor heterogeneity and its role in therapeutic resistance.

Tumor heterogeneity is a fundamental driver of therapeutic resistance across solid malignancies, arising from genetic, epigenetic, phenotypic, spatial, temporal, and microenvironmental diversity. In tumors developing at mucosal barrier sites, these heterogeneous features are further shaped by the unique immunological context of mucosal tissues, where immune tolerance, chronic inflammation, and continuous antigen exposure create permissive environments for immune escape and adaptive resistance. Accumulating evidence indicates that myeloid cell plasticity, including functional diversification of granulocytes, macrophages, monocytes, and dendritic cells, represents a critical interface between tumor-intrinsic heterogeneity and mucosal immune regulation. These myeloid populations contribute to spatially organized immunosuppressive niches, altered antigen processing and presentation, and therapy-induced immune remodeling, collectively influencing responses to chemotherapy, targeted therapy, and immunotherapy. Advances in single-cell sequencing, spatial transcriptomics, multiplex imaging, and liquid biopsy technologies, coupled with artificial intelligence-enabled analytics, have enabled high-resolution mapping of heterogeneous tumor immune landscapes and revealed convergent resistance mechanisms driven by clonal selection, phenotypic plasticity, microenvironmental buffering, and myeloid-mediated immune suppression. In this review, we synthesize mechanistic and clinical evidence across major cancer types, including colorectal and lung cancers as archetypal mucosal tumors, along with broader examples from breast cancer, melanoma, and immunotherapy-treated malignancies. We highlight how heterogeneous cellular states and immune niches influence clinical outcomes. Finally, we discuss emerging translational strategies to overcome resistance, including rational combination regimens, epigenetic and metabolic targeting, adaptive therapy, myeloid reprogramming approaches, and real-time biomarker monitoring. These approaches aim to restore effective anti-tumor immunity while accounting for the unique constraints of mucosal barrier tissue.