ROLE OF TUMOR MICROENVIRONMENT IN GENETIC PROGRESSION

Interaction between Tumor Cells and Surrounding Stroma

The interaction between tumor cells and the adjacent stroma is essential in facilitating tumor growth, notably in iCCA [60-64]. The TME, consisting of stromal cells, extracellular matrix (ECM), immune cells, and blood arteries, actively facilitates tumor growth and spread. Tumor cells release growth factors, cytokines, and matrix metalloproteinases (MMPs) that alter the extracellular matrix (ECM), facilitating cell motility, invasion, and angiogenesis. In iCCA, the stroma undergoes desmoplasia, with fibroblasts, endothelial cells, and immune cells participating in the development of a fibrotic tumor microenvironment [65]. This modified stroma creates an immunosuppressive milieu, constraining anti-tumor immune responses and facilitating cancer cell persistence. Cancer-associated fibroblasts (CAFs) and endothelial cells secrete substances, such as TGF-β and VEGF, which promote fibrosis and angiogenesis. The interaction between tumor cells and the stroma promotes tumor cell invasion, chemoresistance, and metastasis, highlighting the stroma's significance in iCCA pathophysiology and as a potential therapeutic target [66].

Contribution of Immune Cells and Inflammatory Response

Immune cells and the inflammatory response play a crucial role in the advancement of iCCA. Chronic liver inflammation, frequently resulting from illnesses, such as cholangitis or liver cirrhosis, establishes an immunosuppressive tumor microenvironment [67]. Tumor-associated macrophages (TAMs), regulatory T cells (Tregs), and myeloid-derived suppressor cells (MDSCs) facilitate tumor proliferation and metastasis by the secretion of cytokines, such as TGF-β and IL-10, which inhibit immune responses and bolster tumor cell viability. Moreover, neutrophils and dendritic cells can promote cancer cell invasion and angiogenesis, hence advancing iCCA progression [68]. Modulating the inflammatory response may enhance treatment effectiveness and mitigate immune evasion.

Hypoxia-induced Genetic Changes

Hypoxia, a prevalent characteristic of malignancies, triggers genetic alterations that accelerate cancer advancement, particularly in iCCA [69]. Under hypoxic conditions, hypoxia-inducible factors (HIFs) are activated, enhancing the expression of genes associated with angiogenesis, such as VEGF, and glycolysis, such as LDHA, to facilitate tumor survival. Hypoxia induces mutations and epigenetic modifications, facilitating tumor cell invasion and conferring resistance to chemotherapy [70-73]. Moreover, it aids in the selection of cancer stem cells, which exhibit greater resistance to hypoxia-induced stress. Hypoxia-induced genomic alterations engender an aggressive tumor phenotype, facilitating metastasis and resistance to therapy in iCCA [74].

Impact of Angiogenesis on Tumor Development

Angiogenesis, the creation of new blood vessels, is essential in tumor progression, particularly in iCCA. Tumors release pro-angiogenic substances, such as VEGF, which stimulate endothelial cells to generate new blood vessels, thereby providing oxygen and nutrition to expanding tumor masses [75]. This vascular network also enables metastasis by offering a pathway for cancer cells to infiltrate the bloodstream. Angiogenesis facilitates tumor proliferation, viability, and therapeutic resistance by improving nutrient supply and waste elimination. Inhibiting angiogenesis has emerged as a promising therapeutic approach in iCCA, with the goal of depriving tumors of nutrients and diminishing their metastatic potential.