HOXB9 is a member of the Homeobox (HOX) gene family, which plays a crucial role in embryonic development and is involved in the regulation of gene expression during this process. In addition to its role in embryogenesis, HOXB9 has been implicated in various cancers, including breast and prostate cancer. It is overexpressed in breast cancer tissue and is regulated by estrogen, playing a critical role in angiogenesis. HOXB9 overexpression has been shown to stimulate three-dimensional colony formation in soft-agar assays, indicating its role in tumorigenesis. Furthermore, HOXB9 binds to the promoters of various tumor growth and angiogenic factors, regulating their expression, and its homeodomain plays a crucial role in transcriptional regulation and tumorigenesis.