Cancer therapy integrates local and systemic modalities adapted to tumor type, stage, molecular profile, and patient-specific factors. Local control relies on surgery and radiotherapy, each with defined indications and limitations, including the risk of delayed toxicity and secondary malignancies. Because most cancers become life-threatening after metastatic spread, systemic therapy is central and follows a structured architecture of induction, consolidation, and maintenance to reduce tumor burden and prevent relapse. Classical chemotherapy targets DNA replication and mitosis but is limited by toxicity and the emergence of resistant subclones. Modern insights highlight mitochondrial apoptotic priming as the key determinant of chemotherapeutic selectivity. Targeted therapies exploit oncogenic drivers, dysregulated signaling pathways, and epigenetic vulnerabilities through monoclonal antibodies, small-molecule inhibitors, hormone therapies, and chromatin-modifying agents. Precision oncology integrates genomic, transcriptomic, epigenomic, and immunologic biomarkers to match therapies to individual tumor biology. Comprehensive molecular profiling increasingly identifies actionable alterations across cancer types, enabling the use of targeted agents, immunotherapies, and synthetic-lethal approaches. Emerging themes include epigenetic plasticity as a major driver of treatment resistance, metabolic influences on therapy response, and the potential of dietary interventions to augment targeted and immune therapies. Future oncology depends on adaptive, data-driven, multidisciplinary approaches that personalize treatment while accounting for comorbidities, patient context, and long-term survivorship.