BACKGROUND: Small bowel cancer (SBC) is a rare and highly heterogeneous disease in respect to both anatomical distribution and histological morphology. We aimed to conduct a Danish nationwide population-based cohort study of the incidence of, phenotypes of, stage of, synchronous/metachronous cancer occurrence of and survival from SBC during 1994-2010.

METHODS: The study population included all individuals aged 16 years or older living in Denmark during 1994-2010 (n = 7,070,142). Patients with SBC were identified through the Danish Cancer Registry. Incidence rates were calculated overall and according to the anatomical origin and morphological subtype. Patients were followed up from the date of cancer diagnosis to the date of emigration, death or the end of the study (31 December 2010).

RESULTS: SBC was diagnosed in 1088 patients during 1994-2010. The total annual incidence of SBC was 1.10 per 100,000 [95 % confidence interval (CI) 1.04 to 1.17 per 100,000], with an annual percentage change of 1.9 % (95 % CI 0.6-3.1 %, p = 0.003) during the observation period. This increase was mainly explained by an increase in the occurrence of duodenal adenocarcinomas, with an annual percentage change of 7.5 % (95 % CI 4.9-10.2 %, p < 0.001). Further, 29 % of all SBC patients had metastatic cancer at the time of diagnosis and 32 % had one or more synchronous/metachronous cancers. All morphological subtypes were associated with poor 5-year prognoses, in particular duodenal adenocarcinomas, with a 5-year survival rate of only 16 % (95 % CI 12-22 %).

CONCLUSIONS: The incidence of SBC has increased in recent decades, mainly because of a large increase in the incidence of duodenal adenocarcinomas, which are also associated with the poorest prognosis.