We assessed direct biomarkers of aspirin action consisting of the analysis of the extent of acetylation at Serine 529 and Serine 516 of COX-1 and COX-2 (Patrignani et al., 2014; Patrignani et al., 2017; Tacconelli et al., 2020), respectively, in platelets and colorectal tissues of CRC patients randomized to receive aspirin 100, 300 mg/d, or 100 mg/BID for ∼3 weeks. Here, PTGS2 is linked to colorectal carcinoma.