In a preliminary study in healthy subjects, the investigators determined the pharmacokinetic and pharmacodynamic of enteric-coated acetylsalicylic acid (ASA) (Adiro 100 mg, Bayer), and the variability (coefficient of variation), accuracy and precision of a novel biomarker of ASA action, i.e., quantification of the extent of COX-1 acetylation at serine-529, using a stable isotope dilution liquid chromatography multiple reaction monitoring/mass spectrometry (LC-MS) technique.

Now, the investigators will perform a clinical study in individuals undergoing Colorectal cancer (CRC) to validate the hypothesis that that low-dose ASA given once daily is acting primarily by selectively acetylating platelet COX-1 and suppressing its activity throughout the 24-hour dosing interval. In contrast, it is expected that the inhibitory effect on extra-platelet sources of COX-1 will be short-lasting, if any, affecting only partially COX-1, and this effect will be completely reversed at 24 hours after dosing. This is an important point which will strengthen the platelet hypothesis underpinning the apparent adequacy of a 24-hour dosing interval of ASA administration for the anticancer effect detected in cardiovascular trials.

These patients will be stratified into individuals with adenomas/carcinomas (20 to 30%) and patients without clinically detected adenomas/carcinomas (about 70 to 80%).

Inclusion Criteria:

1. Men and women, aged ≥ 18 and ≤ 69.

2. Patients should have an indication for screening colonoscopy

   1. First degree relative of patient with CRC.
   2. Personal history of adenomas.
   3. People older than 50 and FOBT positive

3. Routine hematological and biochemical parameters within the normal range.

Exclusion Criteria:

1. Allergy to ASA or other NSAIDs.
2. Previous use of ASA, NSAIDS, antiplatelet agents, corticosteroids or misoprostol in the previous 15 days and/or anticipated need for these drugs during the study period.
3. Peptic ulcer history or any other gastrointestinal disease that could be considered a contraindication for ASA use without the concomitant use of a proton-pump inhibitor.
4. Subjects with coagulation disorder or serious comorbid condition.
5. Malignancies, excluding CRC, diagnosed in the previous 5 years
6. Cigarette smoking, history of drug or alcohol abuse
7. Pregnant women or breast feeding