CDK7 (cyclin-dependent kinase 7) is a serine/threonine kinase with dual roles in cell cycle regulation and RNA polymerase II-mediated transcription 1. As the catalytic subunit of the CDK-activating kinase (CAK) complex, CDK7 phosphorylates and activates other CDKs (CDK1, CDK2, CDK4, CDK6) during G1/S and G2/M transitions, controlling cell cycle progression 1. In transcription, CDK7 phosphorylates the C-terminal domain (CTD) of RNA polymerase II at serine-5 residues within TFIIH, promoting promoter escape and transcript elongation 2. CDK7 also regulates p53 activation upon DNA damage through direct phosphorylation, establishing a feedback loop that can trigger cell cycle arrest or apoptosis 1. Beyond canonical functions, CDK7 drives oncogenic programs in multiple cancers. In estrogen receptor-positive breast cancer, CDK7 inhibition suppresses c-Myc signaling and cell cycle progression while enhancing apoptosis, particularly in therapy-resistant models 3. CDK7 similarly controls E2F and MYC-driven proliferation in multiple myeloma 4. In small cell lung cancer, CDK7 inhibition induces genome instability and immune activation 5. Metabolically, CDK7 regulates cancer stem cell properties through YAP-mediated LDHD expression in esophageal cancer 6. Dual CDK4/6-CDK7 inhibition shows promise for overcoming treatment resistance in breast cancer 7, making CDK7 an emerging therapeutic target across multiple malignancies.