FAM81B is a nucleus-localized protein with predicted protein-binding capacity 1. While its specific molecular function remains largely undefined, FAM81B expression has been associated with clinical and pathological features in cancer contexts. In breast cancer, FAM81B mRNA expression correlates with PIK3CA mutational status, with increased expression in tumors harboring PIK3CA mutations 1. Additionally, FAM81B expression levels associate with progression-free survival (PFS) in estrogen receptor-positive breast cancer patients receiving aromatase inhibitor therapy, emerging as a potential biomarker for treatment outcome 1. In mesothelioma, FAM81B demonstrates elevated expression in stroma-poor tumors and may have a genomic basis related to tumor-to-stroma ratio, a prognostic parameter 2. FAM81B has also been identified as a candidate variant in familial breast cancer predisposition through exome sequencing, though this particular variant did not co-segregate with disease in the investigated pedigree 3. These findings suggest FAM81B may play a role in cancer biology and treatment response, though direct mechanistic studies are needed to clarify its functional contributions to malignant phenotypes.