In 1969, a remarkable cancer predisposition syndrome was reported by Li and Fraumeni. Using a classical epidemiologic approach, they retrospectively evaluated 280 medical charts and 418 death certificates of children diagnosed with rhabdomyosarcoma in the United States from 1960 to 1964 [1,2]. Five families were identified in whom a second child had developed a soft tissue sarcoma. In addition, a high frequency of diverse cancer types were observed among the first- and second degree adult relatives along one ancestral line of each proband with cancer rates considerably in excess of those expected by chance alone. In addition to soft tissue sarcomas and pre-menopausal breast cancers, carcinomas of the lung, skin, pancreas or adrenal cortex, leukemia, and various brain tumors were also observed. Multiple metachronous primary neoplasms were also observed in several family members. Li and Fraumeni suggested that the occurrence of diverse neoplasms in these families might represent a counterpart of the tendency for a single individual to develop multiple primary tumors, and that these families represented a previously undescribed familial cancer syndrome, with transmission suggestive of an autosomal dominant gene.