Epidemiology and prognosis of synchronous and metachronous colon cancer metastases: a French population-based study

Background: Epidemiological data on synchronous and metachronous metastatic colon cancer are scarce. We assessed epidemiological characteristics and survival in synchronous and metachronous metastatic colon cancer in a French population.

Methods: Our study included 932 cases of metastatic colon cancer diagnosed in 1999-2010 and registered in a population-based cancer registry; 758 were synchronous colon metastases and 174 metachronous metastases from resected primary colon cancers diagnosed in 1999-2005. Univariate relative survival was calculated and a multivariate model with proportional hazard applied to net survival by interval was used.

Results: Mean age at diagnosis was 71.1 years for patients with metachronous metastasis and 71.4 years for those with synchronous metastasis (p=0.818). Patients with metachronous metastasis were more likely to have R0 resection (Odds Ratio: 3.05 [1.96-4.76], p<0.001) than patients with synchronous metastasis. Five-year relative survival was 7.2% for synchronous metastasis and 17.6% for metachronous metastasis (p<0.001), but did not differ significantly for patients with R0 resection (47.3% and 61.5% respectively, p=0.120). For patients not receiving chemotherapy risk of death was significantly lower in the metachronous metastasis group (Hazard Ratio=0.44 [0.32-0.60], p<0.001).

Conclusions: On a population basis, synchronous metastasis is an independent poor prognostic factor in colon cancer. Chemotherapy and resection of all metastatic sites significantly improved the outcome in patients with synchronous metastasis.