BCAS4 (breast carcinoma amplified sequence 4) is a 211 amino acid cytoplasmic protein located at chromosome 20.2 that undergoes amplification and overexpression in breast cancer 1. Originally identified as a novel gene with no homologies to known proteins, BCAS4 can form fusion transcripts with other genes; notably, BCAS3-BCAS4 fusion was detected in MCF7 breast cancer cells and represents a potential oncogenic event 12. In-frame BCAS4 fusion genes (such as BCAS4-AURKA) have been shown to increase viability of breast cancer cells 3. Beyond breast cancer, emerging evidence suggests BCAS4 functions as a competing endogenous RNA (ceRNA) in neurodegeneration, sponging hsa-miR-185-5p to regulate SHISA7 expression during Alzheimer's disease-associated neurofibrillary pathology 4. BCAS4 has also been identified as a significantly mutated gene in head and neck paragangliomas 5 and appears among upregulated proteins in urinary extracellular vesicles from breast cancer patients, suggesting potential utility as a biomarker for cancer screening 6. Additionally, BCAS4 shows promise in molecular classification, contributing to a seven-gene signature for distinguishing grade 3 from grade 4 gliomas with 87.5% classification accuracy 7. The protein is also recognized as a DNA methylation marker in forensic body fluid identification 8.