Quincy is right, mesalamines (5-ASA) and aspirin are not the same. Aspirin can cause internal bleeding while 5-ASAs are anti-inflammatory for UC. But they are related.
Mesalamines are derived from Salicylates which are found in some plants such as white willow bark and wintergreen leaves. Aspirin is also derived from those salicylates which have been used for its health benefits for at least 2,400 years.https://www.ncbi.nlm.nih.gov/pubmed/247106205-Aminosalicylates reduce the risk of colorectal neoplasia in patients with ulcerative colitis:
Seventeen studies containing 1,508 cases of colorectal neoplasia and a total of 20,193 subjects published from 1994 to 2012 were analyzed. 5-aminosalicylates use was associated with a reduced risk of colorectal neoplasia in patients with ulcerative colitis (OR 0.63; 95%CI 0.48-0.84). Pooled OR of a higher average daily dose of 5-aminosalicylates (sulfasalazine ≥ 2.0 g/d, mesalamine ≥ 1.2 g/d) was 0.51 [0.35-0.75]. Pooled OR of 5-aminosalicylates use in patients with extensive ulcerative colitis was 1.00 [0.53-1.89].
Our pooled results indicated that 5-aminosalicylates use was associated with a reduced risk of colorectal neoplasia in patients with ulcerative colitis, especially in the cases with a higher average daily dose of 5-aminosalicylates use.