A set of contiguous and partially overlapping RNA sequences and polypeptides encoded thereby, designated as BS106 and transcribed from breast tissue is described. These sequences are useful for the detecting, diagnosing, staging, monitoring, prognosticating, preventing or treating, or determining the predisposition of an individual to diseases and conditions of the breast such as breast cancer. Also provided are antibodies which specifically bind to BS106-encoded polypeptide or protein, and agonists or inhibitors which prevent action of the tissue-specific BS106 polypeptide, which molecules are useful for the therapeutic treatment of breast diseases, tumors or metastases.