Cancer remains a formidable global health challenge due to its complex pathophysiology and resistance to conventional treatments. In recent years, the convergence of nanotechnology and oncology has paved the way for innovative therapeutic platforms that address the limitations of traditional modalities. This review examines how nanoparticle (NP)-based strategies enhance the efficacy of chemotherapy, radiotherapy, phototherapy, immunotherapy, and gene therapy by enabling targeted delivery, controlled drug release, and tumor-specific accumulation via the enhanced permeability and retention (EPR) effect. We discuss the design and functionalization of various organic, inorganic, and hybrid NPs, highlighting their roles in improving pharmacokinetics, overcoming multidrug resistance, and modulating the tumor microenvironment. Particular emphasis is placed on dual and multimodal therapies, such as chemo-phototherapy, chemo-immunotherapy, and gene-radiotherapy, that leverage nanoparticle carriers to amplify synergistic effects, minimize systemic toxicity, and improve clinical outcomes. We also explore cutting-edge advances in gene editing and personalized nanomedicine, as well as emerging strategies to address biological barriers and immunosuppressive mechanisms in the tumor niche. Despite the undeniable promise of nanoparticle-based cancer therapies, challenges related to toxicity, scalable manufacturing, regulatory oversight, and long-term biocompatibility must be overcome before they can fully enter clinical practice. By synthesizing recent findings and identifying key opportunities for innovation, this review provides insight into how nanoscale platforms are propelling the next generation of precision oncology.