Second Primary Cancers in Subsites of Colon and Rectum in Patients With Previous Colorectal Cancer

Abstract

Compared with the general population, patients with a previous colorectal cancer are at higher risk for a second colorectal cancer, but detailed risk analysis by subsite is scarce. Our goal was to investigate the risk of a second cancer in relation to subsite as a basis for planning surveillance strategies. This was a retrospective analysis of a prospectively designed, population-based cancer registry (The Netherlands Cancer Registry). Patients with a stage I, II, or III colorectal cancer diagnosed between 1989 and 2008 were included. Cumulative incidence, standardized incidence ratio, and absolute excess risk for second primary cancers in subsites of the colon and rectum were estimated for follow-up periods of 2 to 5, 6 to 10, and more than 10 years after the index cancer in patients older than 50 years and in those aged 50 years or younger. A total of 123,347 patients had a first invasive colorectal cancer diagnosed between 1989 and 2008. Of these, 1849 patients (1.5%) had a second colorectal lesion that was found more than 1 year after the initial cancer and diagnosed as a second primary colorectal cancer. In patients older than 50 years, the 20-year cumulative incidence for second cancers was 3.4% in the proximal colon, 1.2% in the distal colon, and 1.2% in the rectum. More than 60% of second cancers occurred within 5 years after the index cancer. The standardized incidence ratio was highest in the proximal-colon (1.9; 95% CI, 1.8-2.0), followed by the distal-colon (1.0, 95% CI, 0.9-1.1), and the rectum (0.9, 95% CI, 0.8-1.0). The corresponding absolute excess risks per 10 000 person years were 9 in the proximal colon, 0.1 in the distal colon, and 1 in the rectum. After 5 years of follow-up, elevated risk was observed only in the proximal colon. A similar risk pattern was observed in patients younger than 50 years. The absolute excess risk for a second cancer in the proximal colon increased over time. The proportion of stage III and stage IV second cancers increased from 31% during the first 5 years of follow-up to 38% after 10 years of follow-up. Limitations of this study included lack of data regarding polypectomy rates and interval of surveillance colonoscopies. Compared with the general population, individuals with previous colorectal cancer have a higher risk for a second cancer in all subsites of the colon and rectum. Among long-term survivors older than 50 years, risk remains elevated only in the proximal colon. Further studies should be encouraged to develop a suitable surveillance method for aging, high-risk, long-term colorectal cancer survivors.