Young patients with colorectal cancer have increased risk of second primary cancers.

OBJECTIVE: Because the number of long-term survivors of colorectal cancer has increased, second primary cancer has become an important issue. However, previous studies were heterogeneous in design, and few data for Asia-Pacific area were available.

METHODS: This was a retrospective population-based study conducted using the national database of the Taiwan Cancer Registry. Patients who have histology-proven primary colon cancer and rectal cancer from 1995 to 2005 were enrolled in this study. All second primary cancer events had to be histology proven. The standardized incidence ratio of second primary cancer was used as an indicator. Standardized incidence ratio was counted as the number of observed second primary cancer divided by the expected number of cancer cases in the general population.

RESULTS: A total of 65 648 eligible index patients were enrolled, and 3810 second primary cancer events were identified. The standardized incidence ratio for all of the patients was 1.03 (95% confidence interval: 0.99-1.06), which implied that the risk of second primary cancer was not significantly elevated in the index patients compared with that of the general population. The standardized incidence ratio for the patients aged <50, 50-70 and >70 years was 2.52 (95% confidence interval: 2.28-2.78), 1.18 (95% confidence interval: 1.12-1.23) and 0.80 (95% confidence interval: 0.76-0.84), respectively. In young patients (aged <50 years), the standardized incidence ratio increase was statistically significant and persisted for over 10 years and this significantly increased across all subgroups. The small intestine, the large intestine, the female genital organs and the lungs were the most common sites of second primary cancer in young patients.

CONCLUSIONS: Young patients with colorectal cancer have an increased risk of developing second primary cancer.