To identify rare mutations and retrospectively estimate the cancer risk of a 45-year old female patient diagnosed with Li-Fraumeni syndrome (LFS), who developed nine primary malignant neoplasms in a period of 38 years, we conducted next-generation sequencing in this patient. Whole-genome and whole-exome sequencing were performed in DNA of whole blood obtained a year prior to the diagnosis of acute myeloid leukemia (AML) and at the time of diagnosis of AML, respectively. We analyzed rare mutations in cancer susceptibility genes using a candidate strategy and estimated cancer risk using the Risk-O-Gram algorithm. We found rare mutations in cancer susceptibility genes associated with an increased hereditary cancer risk in the patient. Notably, the number of mutated genes in p53 signaling pathway was significantly higher than expected (p=0.02). However, the phenotype of multiple malignant neoplasms of the studied patient was unlikely to be caused by accumulation of common cancer risk alleles. In conclusion, we established the mutation profile in a rare case of Li-Fraumeni syndrome, illustrating that the rare mutations rather than the cumulative of common risk alleles leading to an increased cancer risk in the patient.