The risk of metachronous cancers in patients with small-intestinal carcinoid tumors: a US population-based study.

Small-intestinal carcinoids (SIC) are the most common small-bowel malignancies. We sought to determine the risk of developing SIC before and after other primary malignancies (PM) and the prognosis of patients with SIC, with and without another PM. We used the Surveillance, Epidemiology, and End Results database to identify patients diagnosed with SICs between 1973 and 2007. Multiple primary-standardized incidence ratios were calculated as an approximation of relative risk (RR) to explore the association of SICs with metachronous malignancies. Survival analysis was performed using Kaplan-Meier methods and Cox proportional-hazard models. Among 8331 patients with SICs, 2424 (29%) had another PM at some time. The most common sites were prostate (26.2%), breast (14.3%), colon (9.1%), lung/bronchus (6.3%), and bladder (5.3%). Overall, 67% of patients had a PM diagnosed before SIC (pre-SIC), 33% after SIC (post-SIC), and 8% had a PM both before and after SIC. Among the pre-SIC group, the risk of future SIC was increased after cancers of the small bowel (RR 11.86 (95% CI: 6.13-20.72)), esophagus (4.05 (1.10-10.36)), colon (1.39 (1.05-1.81)), kidney (1.93 (1.12-3.09)), prostate (1.38 (1.17-1.62)), and leukemia (2.15 (1.18-3.61)). Among the post-SIC group, there was an increased risk of future PM of the small bowel (8.78 (4.54-15.34)), liver (2.49 (1.08-4.91)), prostate (1.25 (1.0-1.53)), and thyroid (2.73 (1.10-5.62)). Compared to patients with only SIC, those with a PM pre-SIC had worse mean survival (57.9 vs 40.9 months, HR 1.55 (1.42-1.69), P<0.001). In conclusion, almost one-third of patients with SICs have an associated metachronous primary tumor. When these primaries occur prior to (but not after) the SIC diagnosis, the prognosis is worse than with an initial SIC. The type of malignancies associated with SICs may guide future screening efforts.