INTRODUCTION: Cancer remains one of the leading causes of mortality and financial distress worldwide. In South Korea, the government introduced a benefit extension system in 2013 aimed at mitigating the financial strain associated with cancer treatment. However, cancer patients continue to bear significant out-of-pocket (OOP) expenses. This study aims to quantify the incremental healthcare utilization and OOP expenditures incurred by cancer patients in South Korea. METHODS: Utilizing data from the 2019 Korean Health Panel (KHP), we assessed cancer-related healthcare utilization and OOP expenditures. A generalized linear regression model, adjusted for demographic and socioeconomic variables, was employed. Healthcare utilization was measured by hospital admissions, outpatient visits, and emergency room (ER) visits, while OOP expenditures encompassed services including both covered and not covered by the National Health Insurance (NHI) system. RESULTS: Cancer patients experienced 0.39 more hospitalizations, 4.91 additional outpatient visits, and 0.11 more ER visits annually compared to non-cancer patients. Their incremental OOP expenses amounted to 82.8 per year, with 40.2 attributable to inpatient services. Notable variations in healthcare utilization and expenditures were observed across different cancer types. DISCUSSION: Despite the implementation of the benefit extension system, cancer patients continue to face considerable OOP expenses, particularly for inpatient care. With cancer incidence expected to rise, there is a pressing need for more comprehensive healthcare policies that alleviate the financial burden and prioritize cost-effective treatments for cancer patients. CONCLUSION: This study underscores the substantial economic impact of cancer on South Korean patients. Expanding the benefit extension system and promoting cost-effective care strategies are critical to easing the growing financial pressures on cancer patients.