PCIF1 functions as a cap-specific adenosine methyltransferase that catalyzes the formation of N6,2'-O-dimethyladenosine (m6Am) by methylating adenosine at the second transcribed position of capped mRNAs 1. The enzyme is recruited to the early elongation complex of RNA polymerase II via interaction with POLR2A, mediating m6Am formation co-transcriptionally 1. Functionally, m6Am modification negatively impacts cap-dependent translation of methylated mRNAs without affecting mRNA transcription or stability 1. PCIF1 requires cofactors like CTBP2 for optimal catalytic activity and mRNA targeting 2. The protein exhibits context-dependent roles in cancer, generally promoting tumor progression in colorectal cancer, renal cell carcinoma, and head and neck squamous cell carcinoma through regulation of oncogenic pathways 342, while paradoxically inhibiting glioma growth 5. Clinically, PCIF1 expression correlates with poor prognosis in several cancers and influences immunotherapy responses by modulating immune cell activation and tumor microenvironment 63. These findings establish PCIF1 as a critical epitranscriptional regulator with therapeutic potential across multiple cancer types.