Proximal Location of Colon Cancer Is a Risk Factor for Development of Metachronous Colorectal Cancer: A Population-Based Study

This study was undertaken to assess the incidence of 1) metachronous colorectal cancer and 2) subsequent extracolonic cancers, in relation to the location (proximal or distal to the splenic flexure) of the first primary colorectal tumor.

In this population-based study, a cancer registry database was used to identify patients diagnosed with colorectal adenocarcinoma between 1970 and 1999. Patients with familial adenomatous polyposis and those with hereditary nonpolyposis colorectal cancer syndrome were excluded from the study, as were patients with nonepithelial tumors. Location of the first tumor was established according to International Classification of Diseases-Oncology-02 classification. The registry covers a population of 500,000 residents.

A total of 5,006 patients had sporadic adenocarcinoma of the colon or rectum during this period of time, with 1,703 first primary tumors (34 percent) being located proximal to the splenic flexure. One hundred twenty occurrences of second primary colorectal cancer were observed in this population (2.39 percent). The risk for developing a second incidence of primary colorectal cancer was higher in patients whose initial tumor was located in the proximal colon (3.4 percent vs. 1.8 percent; odds ratio, 1.92; 95 percent confidence interval, 1.33–2.77; P < 0.001). The risk for each segment of the large bowel was as follows: cecum, 3.4 percent; right colon, 3 percent; transverse colon, 3.8 percent; left colon, 2.8 percent; sigmoid colon, 1.7 percent; and rectum, 1.8 percent. By contrast, the risk for developing a second, extracolonic tumor did not differ between patients with proximal and distal tumors (13.7 percent vs. 13.4 percent, P = 0.73).

Patients with a first tumor located within the proximal colon are at twice the risk for developing metachronous colorectal cancer. From an epidemiologic standpoint, these data are in accordance with 1) the increasing incidence and 2) the better prognosis of proximal colon cancer in various populations. Our results confirm that proximal colon cancer is a distinct entity, which justifies the reporting of cases of colon cancer according to their location proximal or distal to the splenic flexure.