RESUMO
BACKGROUND: We examined the rate of second primary colorectal cancer (SPCRC) in a cohort of 29 471 patients first diagnosed with colorectal cancer (CRC) from 1987 to 1996, in New South Wales (NSW), Australia. METHODS: The 5-year age group, date and site of first and subsequent CRC diagnoses as well as death dates were obtained from the NSW Central Cancer Registry. The time to SPCRC and standardised incidence ratios (SIRs) were generated. RESULTS: Six hundred and sixty patients (2.1%) developed SPCRCs and the cumulative incidence at 18 years was 5.5%, 95% confidence interval (CI) 4.9% to 6.3%. The risk of SPCRC was increased in patients with a CRC history compared with the general population (SIR = 1.5, 95% CI 1.4-1.6) and inversely related to age at first diagnosis (30-49 years, SIR = 5.1, 95% CI 3.6-7.1 versus >/=80 years, SIR = 1.1, 95% CI 0.9-1.4). The excess absolute risk of SPCRC was greater for females aged 50-69 years at first diagnosis than for males in the same age group. SPCRC was also increased in individuals with right-sided first primaries (SIR = 2.0, 95% CI 1.6-2.4). CONCLUSIONS: The SPCRC rate was increased during the first 5 years after first diagnosis but remained increased for up to 10 years in females, in patients with right-sided cancers and in patients <60 years at first diagnosis. These findings support active surveillance up to 10 years in these risk groups.