FANCB is an X-linked DNA repair protein essential for the Fanconi anemia (FA) pathway. As a core component of the FA complex, FANCB functions upstream in the DNA damage response network to facilitate monoubiquitination of the downstream FA protein FANCD2 1. This process is critical for interstrand crosslink repair and replication-associated double-strand break repair via homologous recombination. FANCB operates within a coordinated pathway including FA proteins (FANCA, FANCC, FANCE, FANCF, FANCG, FANCL) that respond to DNA damage and replication stress 1. Mutations in FANCB cause Fanconi anemia complementation group B, a rare hereditary disorder characterized by genomic instability and cancer predisposition. The X-linked nature of FANCB, combined with X-inactivation mechanisms, means affected individuals have only a single active copy, making this component particularly vulnerable in maintaining genomic integrity 1. Notably, screening of BRCA1/2-negative hereditary breast cancer families found no FANCB mutations, suggesting FANCB does not represent a major contributor to inherited breast cancer susceptibility in this population 2.