 The first was a chromosomal instability pathway thought to be responsible for the adenoma to carcinoma progression, which was characterized by loss of heterozygosity (LOH) on chromosome 5q, 17p and 18q.The second pathway was believed to be the microsatellite instability pathway, which is characterized by increases or decreases in the number of tandem repeats of simple DNA sequences.This type of instability is associated with some specific mutations, including genes involved with DNA mismatch repair and surprisingly, transforming growth factor-beta.