PKMYT1 (protein kinase, membrane associated tyrosine/threonine 1) functions as a negative regulator of cell cycle progression, specifically controlling the G2/M transition by phosphorylating CDK1 when complexed to cyclins 1. The kinase primarily phosphorylates CDK1 at Thr-14, preventing premature mitotic entry and maintaining cell cycle checkpoint control 1. PKMYT1 exhibits dual roles in cancer biology, acting as both a tumor suppressor in normal cells and a pseudo-oncogene in cancer contexts 2. In cancer cells with CCNE1 amplification, PKMYT1 becomes essential for survival, as its inhibition causes unscheduled CDK1 activation and premature mitosis during DNA synthesis 1. The protein contributes to chemotherapy resistance in osteosarcoma by phosphorylating NPM1 at S260, which impairs DNA damage response factor recruitment including BRCA1, RAP80, and RAD51 3. PKMYT1 also promotes cancer stem cell maintenance in non-small cell lung cancer through Wnt signaling pathway activation 4. Therapeutically, selective PKMYT1 inhibitors like RP-6306 show promising efficacy in CCNE1-amplified tumors and synergize with conventional chemotherapies 53. The kinase represents a compelling target for precision cancer therapy, particularly in tumors with specific genetic vulnerabilities.