MED19 is a Mediator complex subunit that functions as a transcriptional coactivator bridging gene-specific regulatory proteins to RNA polymerase II machinery 1. Beyond its canonical role in mediating transcription factor-dependent gene expression 2, MED19 possesses a nucleolus-localized, Mediator-independent function regulating ribosomal RNA 2'-O-methylation and IRES-dependent translation of oncogenic genes including c-Myc 3. In prostate cancer, MED19 promotes androgen-independent growth by cooperating with ELK1 to enhance androgen receptor occupancy and activate MAOA expression 1. MED19 is essential for white adipogenesis and adipose tissue maintenance by mediating PPARγ-dependent gene expression 2. MED19 overexpression is associated with advanced hepatocellular carcinoma features and independently predicts poor prognosis 4. Clinically, MED19 knockdown inhibits proliferation and tumorigenesis across multiple cancer types—hepatocellular carcinoma, prostate cancer, and colorectal cancer—through cell-cycle arrest and apoptosis induction 567. In cervical cancer, MED19 contributes to radioresistance and can be targeted by miR-4778-3p 8. MED19 represents a potential therapeutic target and prognostic biomarker linked to immune landscape and immunotherapy response in hepatocellular carcinoma 4.