Cancer recurrence is the reappearance of malignant disease following a period of remission after initial treatment, manifesting at the primary site (local), adjacent tissues or lymph nodes (regional), or distant locations (distant). As a central concept in oncology research and clinical practice, it investigates the underlying biological mechanisms of residual disease, identifies predictive risk factors influenced by tumor characteristics and treatment efficacy, and guides the development of strategies for post-treatment surveillance, early detection, prevention, and subsequent therapeutic interventions, critically impacting patient prognosis and long-term outcomes.