Data collection

Data collected included demographics (age and sex), date of diagnosis, tumor location, clinical stage (JPS TNM classification [16]), treatment, cause of death, and outcome. Some differences in the TNM classification between the JPS and UICC staging systems with respect to tumor factors (T) and lymph node metastases (N) need to be noted. Briefly, T4 in UICC indicates tumor invasion limited to the trunk of the celiac artery or superior mesenteric artery, whereas invasion to any major vessels, neural plexus, or adjacent organs are included in the JPS classification. Positive lymph node metastasis in UICC is designated N1, while in JPS, various grades are used depending on the distance from the main tumor (N1, N2, or N3).