Metachronous colorectal cancer in Taiwan: Analyzing 20 years of data from Taiwan Cancer Registry

Background: The risk of metachronous colorectal cancer in patients with colorectal cancer is higher than the rate of sporadic colorectal cancer in the average population. We conducted a large-scale, population-based study, with many more clinical cases than in previously published studies, to calculate the incidence of metachronous colorectal cancer. Methods: This is a retrospective study based on data obtained from the Taiwan Cancer Registry from 1988 to 2007. Between 1988 and 2002, we analyzed 70,906 patients who were diagnosed with colon or rectal cancer and traced the occurrence of metachronous lesions with at least 5 years of follow-up. Results: Of these patients, 1,192 (730 males, 462 females; mean age 62.73 ± 12.92 years) developed metachronous cancers. The 15-year cumulative incidence of metachronous cancer was 1.68%. Within 2 years of the index cancer, 51.69% of the metachronous cancers appeared, and 61.27% of the metachronous cancers appeared within 3 years. Conclusions: Most metachronous lesions were noted within 3 years of initial diagnosis of the index cancer. Surveillance colonoscopy to ensure the absence of metachronous disease is essential for patients after curative surgery within 1 year, especially for those patients who did not receive complete colonoscopy before their first operation for colorectal cancer.