Dear Editor: An intra-individual somatic variation (ISV) is described as the genetic difference among different tissues of the same individual. ISV increases with age, may not manifest a defined phenotype, and is associated with neurological, hematological, and immune disorders, especially with cancer.1 To analyze possible ISV in Mexican patients with colorectal cancer (CRC), we studied the polymorphism rs669 (c.2998 A>G, p.Ile1000Val) of the A2M gene, which encodes for the alpha-2 macroglobulin protein, a protease inhibitor involved in tumor progression and proliferation.2 This variant is located near a thioester site, which is necessary for the inhibitory function of the protein.