A population-based comparison of adenocarcinoma of the large and small intestine: insights into a rare disease.

BACKGROUND: Because of its rarity, adenocarcinoma of the small intestine is frequently compared to adenocarcinoma of the colon, although the validity of this comparison is not known.
METHODS: Patients with small and large bowel adenocarcinoma (SBA and LBA) diagnosed between 1988 and 2007 were identified from the Surveillance, Epidemiology, and End Results registry. Age-standardized incidence and mortality rates were determined. Cancer-specific survival (CSS) stratified by stage and by number of assessed lymph nodes was calculated.
RESULTS: A total of 4518 and 261,521 patients with SBA and LBA, respectively, were identified. In comparison to LBA, patients with SBA were younger and presented with disease of higher stage and histologic grade. The age-standardized incidence rates decreased for LBA (-1.24% per year) but increased for SBA (+1.47% per year). Although age-standardized mortality rates decreased for both LBA and SBA, the decreases were more pronounced for LBA. Five-year CSS was worse for resected SBA compared with resected LBA, although this difference diminished when comparing cases having eight or more lymph nodes assessed. The relative reduction in CSS when selecting eight or more lymph nodes was much greater for duodenal as opposed to jejunal/ileal subsite of the small bowel. With nodal selection the absolute difference in CSS between LBA and SBA for stages I, II, and III was 13, 15.9, and 18.5%, respectively.
CONCLUSIONS: Adequate nodal assessment is much less common in SBA than LBA; and it appears that SBA, in particular duodenal adenocarcinoma, is understaged. Even after corrections to minimize the effect of stage migration and inadequate lymph node evaluation, SBA demonstrated distinctly worse CSS than LBA.