OBJECTIVES:
Primary
* To assess the effect of selenium on colorectal adenoma (CRA) occurrence.
* To assess the effect of selenium on number, location, size, histologic type, and degree of dysplasia of CRA.
* To assess the effect of selenium on colorectal cancer (CRC) incidence.
Secondary
* To assess the effect of vitamin E on CRA occurrence.
* To assess the effect of vitamin E on CRC incidence.
Tertiary
* To explore the effect modification of selenium and vitamin E by aspirin on CRA occurrence.
* To explore the effect modification of selenium and vitamin E by body mass index.
OUTLINE: This is a multicenter study.
Endoscopically obtained tissue samples are reviewed by study pathologists to confirm the presence (or absence) of a colorectal adenoma (CRA). If a CRA is present, the number, location, size, histology, and degree of dysplasia are documented. The CRA is also reviewed to exclude a diagnosis of colorectal cancer.
Additional data, including aspirin use, height and weight, date of birth, and other demographic and baseline characteristics, is also obtained. Participants' medical records are reviewed periodically.
Participants are followed annually.
