Li-Fraumeni Syndrom (LFS) is a rather rare disease, fewer than 100 families in the world suffer from this hereditary proneness to tumors of all sorts of tissues. Neatly, p53 is the gene mutated in this case, it comes not so surprising that both germ-line and somatic p53 mutations predispose to a very wide range of tumors. And almost half of all human cancers are involved with p53 mutations. However, p53 mutation in LFS is always very restricted in the third of the p53 exons while somatic mutations can occur anywhere. A possible explanation might be that the third exon is the only region where mutations in p53 is not lethal in embryo development. The offsprings are tumor-prone but they develop normally into adult.