Li Fraumeni Syndrome (LFS) is a devastating autosomal dominant cancer predisposition syndrome characterized by early onset cancers including in children, multiple primary tumors, and predisposition to a wide range of tumors, attributable to germline mutations in the TP53 gene. There have been many efforts to define clinical criteria for testing for LFS, but they fail to identify most LFS cases, limiting effectiveness of LFS screening. We have established a collaboration with 3 Sister Institutions with a strong history in study of distinct LFS populations to develop an extended database from the US, Brazil and Australia, to develop a quantitative tool to assist in LFS identification, an urgent need now that an effective comprehensive screening program has been shown to prove survival benefit. The overall objective is to improve the clinical characterization and management of LFS families based on a Mendelian model development to improve the identification of LFS kind reds.