Along recent economical development of Korea, the average life span of the Korean people has been increased dramatically. As the lifespan is increased, average occurrence rate of all cancers have increased from 219.9 cases per 100,000 in 1999 to 252.5 cases per 100,000 in 2005. Even though many reports show different results, it is normally accepted that the occurrence rate of carcinoma of unknown origin (CUP) is 2-6%. 

However, only 1,500 cases of CUP were reported annually in Korea according to the National Health Insurance records and may hold less significant epidemiologic values. Some experts say that the reason why only a small number of CUP is reported is because the Health Insurance Review Agency’s "Drug Guideline for Cancer Patients" does not include CUP. Therefore, when a patient is diagnosed with CUP, the economical burden on the patient is increased dramatically. 

As of result, many of the CUP patients are being treated under a different diagnosis. This results in underestimating the importance of CUP in the Korean population and inadequate allocation of medical resources. Even though CUP is known to have bad prognosis, various adequate treatments may be performed to increase the patient’s survival. It is important to provide an adequate socioeconomic support to apply effective treatment plans for CUP patients. Therefore, systematic reference analysis was performed to evaluate the effects of initial treatment.