Abundant epidemiological evidence indicates that regular and long term use of aspirin is
associated with a significant reduction in the incidence of colorectal cancer (CRC). The long
duration of aspirin needed to prevent CRC is believed to be due to inhibition of precursor lesions
known as adenomas, whose recurrence is inhibited by aspirin in randomized trials. Aspirin intake
has also been associated with a statistically significant improvement in patient survival after
curative resection of CRC in large observational studies. In these cohorts, the survival benefit of
aspirin was shown to depend upon the level of cyclooxygenase-2 (COX-2) expression in the
primary CRC. More recent analysis of patient tumors from these observational cohorts suggests
that the benefit of aspirin may be limited to specific molecular subtypes. Aspirin intake following
CRC resection was associated with a significant improvement of survival in patients whose tumors
carried mutant, but not wild-type, copies of the phosphatidylinositol 3-kinase (PI3KCA) gene,
especially tumors that overexpressed COX-2. A mechanistic explanation is suggested by the
finding that inhibition of COX-mediated prostaglandin E2 synthesis by aspirin attenuates PI3K
signaling activity that is known to regulate cancer cell proliferation and survival. Aspirin has also
been shown to reduce the incidence of CRCs bearing wild-type, but not mutant alleles of the
BRAFV600E oncogene. While provocative, the potential utility of these molecular markers for
predicting aspirin efficacy awaits prospective evaluation in clinical trials. If validated, these
finding may support a personalized approach to using aspirin for the therapy of CRC.