The lifelong risk of metachronous colorectal cancer justifies long-term colonoscopic follow-up.

BACKGROUND: The aim of this study was to calculate the risk of metachronous colorectal cancers, to specify their characteristics and potential risk factors in a well-defined French population over a 27-year period.

PATIENTS AND METHODS: The 10,801 patients who had colorectal cancers totalled 61,879 person-years of follow-up. The actuarial method was used to obtain crude metachronous colorectal cancer rates. Standardised incidence ratios (SIRs) were calculated.

RESULTS: The cumulative rate of metachronous colorectal cancer was 1.8% at 5 years, 3.4% at 10 years and 7.2% at 20 years. The incidence of metachronous colorectal cancer following a first colorectal cancer was higher than expected (SIR: 1.5 [1.3-1.7] p<0.001). It remained greater throughout the study period, significantly only between the first and the fifth years following diagnosis (SIR: 1.9 [1.6-2.3] p<0.010). As compared to solitary cancers, metachronous cancers were diagnosed at earlier stages (23.5% versus 40.9% were stage I, p<0.001). None of the personal and tumour characteristics were predicting factors for the development of metachronous colorectal cancer.

CONCLUSION: Patients with colorectal cancer are at greater risk of developing a metachronous colorectal cancer. Among them, no predicting factors for the development of metachronous tumours were found. Thus lifelong colonoscopic surveillance is needed.