Lessons Learned in Practice with Li-Fraumeni Syndrome: LFS-Related Breast Cancer Treatment Strategy and Establishment of a Surveillance System.

We herein present the case of a 33-year-old woman with no family history of metachronous bilateral breast cancer and osteosarcoma, diagnosed with Li-Fraumeni syndrome (LFS), which is a rare autosomal dominant hereditary cancer syndrome associated with a germline variant. She was diagnosed with left distal femoral osteosarcoma at the age of 16, and metachronous bilateral breast cancer at the ages of 29 and 33. When the third cancer was diagnosed, a hereditary tumor syndrome was suspected and the patient was referred to our genetic outpatient clinic. There was no family history of the 'core' cancers for LFS, but since the patient met Chompret's criteria, germline genetic testing was performed with the patient's will. A pathogenic variant, :c.216dupC (p.Val73ArgfsX76) was found in exon 4 of the gene. This case is didactic because radiotherapy was performed on the first breast cancer before the diagnosis of LFS was made; radiation should be avoided if there are other options in LFS because of the inability to repair DNA damage. As a lesson learned, oncologists reaffirmed the importance of being aware of hereditary tumors from the keywords "multiple," "young," "familial," and "rare," and consulting the genetic department. In addition, surveillance using whole-body magnetic resonance imaging is recommended in LFS. However, this system is not yet provided nationwide, but we have newly settled it in our hospital.