Background: Overall, the incidence of colorectal cancer appears to be stable or diminishing. However, based on our practice pattern, we observed that the incidence of rectal cancer in patients under 40 is increasing and may be associated with a prominence of signet-ring cell histology.
Objective: The aim of this study was to verify the rising trend in rectal cancer in patients under 40 and describe the histology prominent in that cohort.
Design: This is a retrospective cohort study.
Setting and patients: We performed a retrospective cohort study of all patients diagnosed with rectal adenocarcinoma from 1980 to 2010 using the Surveillance, Epidemiology, and End Results cancer registry.
Main outcome measures: Rectal cancer incidence, histology, and associated staging characteristics were the primary outcomes measured.
Results: Although the incidence of rectal cancer for all ages remained stable from 1980 to 2010, we observed an annual percent change of +3.6% in the incidence of rectal cancer in patients under 40. The prevalence of signet cell histology in patients under 40 was significantly greater than in patients over 40 (3% vs 0.87%, p < 0.01). A multivariate regression analysis revealed an adjusted odds ratio of 3.6 (95% CI, 2.6-5.1) for signet cell histology in rectal adenocarcinoma under age 40. Signet cell histology was also significantly associated with a more advanced stage at presentation, poorly differentiated tumor grade, and worse prognosis compared with mucinous and nonmucinous rectal adenocarcinoma.
Limitations: The study was limited by its retrospective nature and the information available in the Surveillance, Epidemiology, and End Results database.
Conclusions: Despite a stable incidence of rectal cancer for all ages, the incidence in patients under 40 has quadrupled since 1980, and cancers in this group are 3.6 times more likely to have signet cell histology. Given the worse outcomes associated with signet cell histology, these data highlight a need for thorough evaluation of young patients with rectal symptoms.