CDK12 (cyclin-dependent kinase 12) is a transcription-associated kinase that plays a crucial role in regulating gene expression and maintaining genomic stability. CDK12 phosphorylates the C-terminal domain of RNA polymerase II, thereby controlling transcription elongation and RNA splicing processes 1. The kinase is particularly important for DNA damage response, as CDK12 inhibition triggers intronic polyadenylation that suppresses expression of core DNA damage response proteins, creating a 'BRCAness' phenotype with deficient DNA repair 2. CDK12 mutations are frequently observed in aggressive cancers, particularly prostate cancer, where frameshift loss-of-function mutations characterize a distinct subtype with poor prognosis 34. In metastatic prostate cancer, CDK12 mutations correlate with specific structural variations, including tandem duplications 5. Therapeutically, CDK12-deficient tumors show synthetic lethality with PARP inhibitors, with clinical evidence showing PSA responses in 55% of prostate cancer patients with biallelic CDK12 mutations treated with rucaparib 3. Additionally, CDK12 represents a potential therapeutic target itself, as selective dual CDK12/CDK13 inhibitors demonstrate efficacy against triple-negative breast cancer 2, and molecular glue degraders can deplete cyclin K to disrupt CDK12 function 6.