Many families first notice Li-Fraumeni syndrome 1 when a close relative is diagnosed with cancer at an unusually young age, prompting doctors to ask about patterns across the family tree. Sometimes the first signs of Li-Fraumeni syndrome 1 appear as a rare or early cancer in a child or young adult—such as soft tissue sarcoma, brain tumor, adrenocortical tumor, or early breast cancer—which leads to genetic testing. In other cases, how Li-Fraumeni syndrome 1 is first noticed comes through proactive screening or genetic counseling after a concerning family history, even before any symptoms appear.