title: Clinical characteristics of colorectal cancer patients with a second primary cancer.
abstract: OBJECTIVE
  The incidence of colorectal cancer is increasing due to a westernized dietary lifestyle, and improvements in treatment and diagnostic tools have resulted in more patients being confirmed of having multiple primary cancers. However, studies regarding multiple primary cancers are insufficient. In this study, the clinical aspects of patients with primary multiple cancers, including colorectal cancers, were investigated, and the results were compared to those of patients with primary colorectal cancer only.
  
  
  METHODS
  Seven hundred eighteen patients who received surgery for colorectal cancer between March 2003 and September 2012 in CHA Medical Center were enrolled. A retrograde cohort was done for comparison of the two groups: those with and those without multiple primary cancer. The analysis was done according to sex, age, tumor location, tumor size, metastatic regional lymph-node number, vascular/lymphatic microinvasion, staging, tumor markers, microsatellite instability, and C/T subgroup of polymorphism in methylenetetrahydrofolate reductase.
  
  
  RESULTS
  Of the 718 subjects, 33 (4.6%) had multiple primary cancers: 12 (36.4%) synchronous and 21 (63.6%) metachronous. The malignancy most frequently accompanying colorectal cancer was gastric cancer, followed by thyroid, prostate, and esophageal malignancies in that order. In the comparison between groups, mean age, tumor location, and microsatellite instability showed statistically significant differences; others parameters did not.
  
  
  CONCLUSIONS
  The incidence of multiple primary cancers, including colorectal cancer, is increasing. Therefore, defining the characteristics of patients with multiple primary cancers is crucial, and those characteristics need to be acknowledged in the follow-up of colorectal cancer patients.
authors.affiliation: Department of Surgery, CHA University College of Medicine, Seongnam, Korea.
authors.forename: Jin Woo
authors.initials: JW
authors.lastname: Lee
authors.affiliation: Department of Surgery, CHA University College of Medicine, Seongnam, Korea.
authors.forename: Jong Woo
authors.initials: JW
authors.lastname: Kim
authors.affiliation: Institute for Clinical Research, CHA University College of Medicine, Seongnam, Korea.
authors.forename: Nam Keun
authors.initials: NK
authors.lastname: Kim
keywords: Colorectal neoplasms; Multiple primary cancer