Concerning molecular biology, the main abnormalities reported in classic fibromas are copy number alterations (CNA) in 88% of the cases, with trisomy or tetrasomy of chromosome 12 as the most prevalent CNA (63%), followed by gain of chromosomes 9 or 9q (50%), 18, and 21 (20% for each) [8,37,38], and a loss of heterozygosity (LOH) at 9q22.3 (proximal PTCH1) in 25% of the cases. Here, PTCH1 is linked to fibroma.