UBFD1 (Ubiquitin Family Domain Containing 1) is a polyubiquitin-binding protein containing ubiquitin-like structural domains that are widely involved in protein degradation and cell signaling. This protein shows aberrant expression in a variety of cancers, especially in estrogen receptor (ER)-positive breast cancer, where high expression of UBFD1 is closely associated with poor prognosis of patients, and is considered as a potential prognostic biomarker and therapeutic target. In addition, UBFD1 was also found to be associated with MYC-mediated tumor aggressiveness in T-cell acute lymphoblastic leukemia (T-ALL), which functionally involves the endoplasmic reticulum-associated degradation (ERAD) pathway. UBFD1 is also expressed in inner ear hair cells and ear epithelial cells, suggesting that it may play a role in hearing-related diseases.