Temporal trend in relative risk of second primary colorectal cancer

BACKGROUND: Patients with colorectal cancer (CRC) are at a higher risk for developing a second primary. Factors (such as survival rate, rate of receipt of surveillance procedures, and the overall incidence of CRC) with potential impact on the risk for second primary CRC have changed over the last three decades. Thus, it is likely that the risk for second primary CRC also has changed over the years. OBJECTIVES: We used the Surveillance, Epidemiology, and End Results public-use database to assess whether the relative risk of second primary CRC has changed in patients with initial primary CRC. METHODS: The temporal trend in the standardized incidence ratio (SIR) for a second primary CRC was estimated. Also, the clinical features of the second primary CRC were compared in two subgroups based on the year of diagnosis of the first primary CRC: Group A (1973-1977) and Group B (1988-1992). RESULTS: During the period of 1973 to 2002, 216,751 patients developed a primary CRC and over a follow-up period of 1,250,687 person-years, 5,595 of these patients developed a second primary CRC, with an SIR of 1.36 (95% CI 1.32-1.39). In a Cox regression model, the period of diagnosis of the first primary CRC was an independent risk factor for a subsequent primary CRC, with a relative hazard of second colon cancer in Group B compared with Group A being 1.18 (95% CI 1.06-1.31), after controlling for age at diagnosis, site, stage of first primary, gender, and race. CONCLUSION: The relative risk of the second primary CRC has increased since early 1990s. These subsequent cancers are being diagnosed at an earlier stage. Increased surveillance may be one of the factors contributing to this temporal difference.