Cancer remains one of the leading causes of mortality worldwide, and despite advancements in therapeutic strategies—including chemotherapy, radiotherapy, immunotherapy, surgery, hormone therapy, and targeted therapy—a definitive cure remains elusive. In recent years, tumor-derived extracellular vesicles (TD-EVs) have garnered attention due to their critical roles in tumorigenesis, angiogenesis, and metastasis. Generated via biogenesis pathways involving the endosomal sorting complex required for transport (ESCRT), TD-EVs facilitate diverse mechanisms that promote tumor growth and survival. These include the induction of epithelial–mesenchymal transition (EMT), stimulation of angiogenesis, suppression of natural killer (NK) and T cell activity, promotion of M2 macrophage polarization, and facilitation of metastasis. Beyond their tumor-promoting functions, TD-EVs also hold promise as diagnostic and therapeutic tools. For example, EV PD-L1 has emerged as a biomarker for the liquid biopsy, reflecting tumor immune evasion, while engineered TD-EVs loaded with therapeutic cargos such as siRNAs or chemotherapeutic agents have shown potential in targeted tumor delivery. Their presence in bodily fluids and selective enrichment of tumor-specific cargo position them as valuable candidates for liquid biopsy applications, enabling non-invasive monitoring of disease progression and treatment responses. Furthermore, engineered TD-EVs are being explored as delivery systems for chemotherapeutics, RNA interference molecules, and gene-editing tools. Despite these advances, different challenges hinder the clinical translation of TD-EV-based applications. These include the heterogeneity of EV populations, lack of standardized isolation and characterization protocols, and difficulty in distinguishing TD-EVs from normal EVs in complex biological samples. Key obstacles also include the pronounced heterogeneity of EV populations and the lack of standardized isolation and characterization protocols. This review explores the multifaceted roles of TD-EVs in cancer biology and their potential utility in diagnosis, prognosis, and therapeutic intervention.