Second primary cancers in subsites of colon and rectum in patients with previous colorectal cancer

Background:
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.
Objective:
Our goal was to investigate the risk of a second cancer in relation to subsite as a basis for planning surveillance strategies,.
Design, setting, and patients:
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.
Main outcome measures:
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.
Results:
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:
Limitations of this study included lack of data regarding polypectomy rates and interval of surveillance colonoscopies.
Conclusions:
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.