Risk of extracolonic second primary cancers following a primary colorectal cancer: a systematic review and meta-analysis.

PURPOSE: The purpose of the study is to assess the global risk of extracolonic secondary primary cancers (SPCs) in patients with colorectal cancer (CRC). METHODS: Studies of SPC in patients with CRC were included if they reported the standardised incidence ratio (SIR) for extracolonic SPCs in patients with CRC compared with the general population. Pooled summary estimates were calculated using a random-effects model. RESULTS: A total of 7,716,750 patients with CRC from 13 retrospective cohort studies that reported extracolonic SPC incidence were included. The overall risk of several SPCs was significantly higher in patients with CRC compared with the general population, including cancers of the urinary bladder (pooled SIR 1.19, 95% confidence interval (CI) 1.06-1.33; p = 0.003), female genital tract (1.88, 1.07-3.31; p = 0.03), kidney (1.50, 1.19-1.89; p = 0.0007), thorax (lung, bronchus and mediastinum) (1.16, 1.01-1.32; p = 0.03), small intestine (4.26, 2.58-7.01; p < 0.0001), stomach (1.22, 1.07-1.39; p = 0.003), and thyroid (1.40, 1.28-1.53; p < 0.0001), as well as melanoma (1.28, 1.01-1.62; p = 0.04). There was also a decreased risk of developing cancer of the gall bladder (0.75, 0.60-0.94; p = 0.01). CONCLUSION: Patients with CRC had a significantly increased risk of extracolonic SPCs compared with the general population. These findings highlight the need to develop research strategies for the management of second primary cancer in patients with CRC.