Cyclin K is a regulatory subunit of cyclin-dependent kinases (CDKs), specifically CDK12 and CDK13, and plays a role in transcription regulation and cell cycle control. It is involved in various cellular processes, including DNA damage response, mitosis, and pre-replicative complex assembly, which are critical for both cancer cell growth and therapeutic resistance. Cyclin K is expressed in a homeostatic manner under normal physiological conditions, with high expression in testes and embryonic stem cells, and its expression decreases with cell differentiation. However, Cyclin K expression is often dysregulated in cancer, leading to its overexpression in various types of tumors, including prostate, breast, lung, and colorectal cancers.