A foundational modality in oncology involving the physical excision of a tumor and surrounding tissue. The primary goal is the complete removal of localized cancer (R0 resection). It can be diagnostic (biopsy), staging (determining the extent of disease), curative, debulking (reducing tumor volume), or palliative (relieving symptoms like obstruction). Surgical oncology requires meticulous planning to achieve clear margins while preserving organ function as much as possible.