Abstract: The invention is directed to polynucleotides encoding ?-parvin, a newly identified tumor suppressor gene the alteration of which is involved in the occurrence of breast cancer in a patient, as well as to corresponding expressed polypeptides. The invention also concerns diagnostic methods using the ?-parvin polynucleotides and/or peptides and embodiments thereof as diagnostic or therapeutic tools for breast cancer or in assays to identify pharmacological agents for the treatment of breast cancer.