LFS is caused by germline TP53 mutations and is known to increase the risk of developing breast cancer.16) Furthermore, it has been suggested that breast cancers arising in the context of pathogenic TP53 mutations are more likely to exhibit HER2 amplification.17) Considering the rarity of HER2-positive subtype male breast cancer patients, it cannot be ruled out that this case may have harbored a pathogenic TP53 mutation. Here, TP53 is linked to Li-Fraumeni syndrome.