TMSB15A (thymosin beta 15A) is an X-linked gene that plays a role in cytoskeletal organization by binding to and sequestering actin monomers (G-actin), thereby inhibiting actin polymerization and potentially regulating cell migration. Beyond its canonical actin-binding function, TMSB15A has emerged as a significant biomarker and therapeutic target in multiple cancer types. In triple-negative breast cancer (TNBC), TMSB15A expression strongly predicts pathological complete response to neoadjuvant chemotherapy, with high expression associated with improved chemotherapy response rates 1. TMSB15A is identified as a biomarker for carboplatin response in TNBC patient-derived xenografts 2 and demonstrates translational potential across clinical datasets. In gastric cancer, TMSB15A is significantly overexpressed and associated with poor prognosis, advanced tumor stages, and lymph node metastasis; functional studies show that TMSB15A knockdown reduces cell proliferation, migration, and invasion, implicating it in tumorigenesis via IL-6/JAK/STAT3, TGF-β, and Hedgehog pathways 3. TMSB15A is also upregulated in nasopharyngeal carcinoma and hepatocellular carcinoma with prognostic significance 45. Notably, TMSB15A is dispensable for male fertility in mice 6, suggesting tissue-specific functions in cancer biology rather than reproductive development.