FAAP100 (Fanconi anemia-associated protein 100, also designated FANCX) is a core component of the FA core complex essential for interstrand crosslink (ICL) repair. It forms a catalytic module with FANCB and FANCL, the E3 ubiquitin ligase responsible for monoubiquitination of FANCD2 and FANCI, critical steps in FA pathway activation 1 2. FAAP100 regulates the stability and nuclear translocation of this BLP100 subcomplex, enabling chr17 recruitment necessary for ICL repair 1. Loss of FAAP100 function results in severe FA characterized by developmental abnormalities, pancytopenia, and early lethality, making FAAP100 deficiency among the most severe FA phenotypes 3 1. Beyond Mendelian FA, FAAP100 dysregulation is implicated in cancer progression. Pan-cancer analyses reveal FAAP100 upregulation correlates with poor survival, enhanced cell proliferation and migration, and reduced apoptosis in lung adenocarcinoma and other cancers 4. FAAP100 overexpression associates with copy number amplification and promoter hypomethylation, alongside increased immune cell infiltration and checkpoint molecule activity 4. FAAP100 also appears as a modifier locus in strabismus genetics 5. These findings establish FAAP100 as both a critical FA pathway component and a potential cancer biomarker and therapeutic target.