The invention provides a human E25a protein which is upregulated in cancerous cells, including those of hormone refractory prostate cancer, colon cancer, breast cancer or other cancers of epithelial origin. The invention also provides nucleic acid molecules encoding E25a protein, nucleic acid probes which hybridize with nucleic acid molecules encoding E25a protein, and antibodies which bind E25a protein. E25a protein and its related molecules can be useful as diagnostic markers of cancer, including hormone refractory prostate cancer, and as specific therapeutic targets in this disease. The invention also provides methods for diagnosing cancer, including hormone refractory prostate cancer.