MAP9 (microtubule-associated protein 9) is a conserved vertebrate protein essential for organizing the bipolar mitotic spindle and regulating microtubule dynamics. Structurally, MAP9 contains MAP, MIT-like, and THY domains in its C-terminal region, with two main coiled-coil regions, and is approximately 110 kDa in size 1. The protein localizes to the mitotic spindle and cytoplasmic microtubules during the cell cycle, where it functions in bipolar spindle assembly, mitosis progression, and cytokinesis 2. MAP9 expression is particularly high in brain and testis tissues 1 and is regulated by phosphorylation in a developmental and context-dependent manner 3. Clinically, MAP9 functions as a tumor suppressor in multiple cancer types. In hepatocellular carcinoma, MAP9 is frequently silenced through promoter hypermethylation, and its downregulation correlates with poor survival and increased recurrence 4. MAP9 suppresses tumorigenesis by inhibiting ERCC3, a nucleotide excision repair gene 4. In colorectal cancer, MAP9 is downregulated compared to normal tissue 5, whereas in EBV-associated gastric carcinoma, MAP9 acts as a tumor suppressor by inhibiting cell growth and inducing apoptosis 6. Notably, a genome-wide association study identified MAP9 (Chr4.1) as associated with female-specific pulse pressure traits, suggesting pleiotropic cardiovascular effects 7. Conversely, in bladder cancer, MAP9 exhibits protumor activities through TGF-β1 pathway activation 8.