Cytogen Corporation announced the presentation of data demonstrating the expression of prostate-specific membrane antigen (PSMA) in cancer of the kidney.

In the study, independent investigators at the Cleveland Clinic evaluated PSMA expression in normal kidneys and tissue samples from both benign and malignant renal lesions using a tissue microarray. Specimens from 60 normal kidneys and 99 renal neoplasms of various cell types were immunostained with the vascular endothelial marker CD34 and an antibody to PSMA. PSMA expression in tumour-associated neovasculature was tested in triplicate and scored for staining intensity and percentage of vessels. PSMA was not expressed in any vascular structures of normal kidneys though it was detected in the brush border of proximal tubules. In renal neoplasms, PSMA was only detected in the tumour neovasculature.

"PSMA represents an excellent target for prostate and potentially other cancers," said Warren D.W. Heston, director, research program in prostate cancer at The Cleveland Clinic Foundation and one of the authors of the study. "In addition to being abundantly and preferentially expressed on the surface of prostate cancer cells, PSMA is also present on endothelial cells of new blood vessels that supply most other solid tumours. Our study results demonstrating the expression of PSMA in kidney cancer justify continued exploration of both imaging and therapeutic approaches that recognize this unique target," he added.

"This data emphasizes the growing relevance of PSMA as a tumour marker and suggests that it may have wider application than just prostate cancer," noted Michael J. Manyak, VP of medical affairs for Cytogen. "These findings may provide a means to differentiate renal tumours and also a method to evaluate possible recurrence in patients who undergo renal ablative procedures or partial nephrectomy for malignancy," he added.

PSMA is a protein abundantly expressed on the surface of prostate cancer cells, with an increased expression in high-grade cancers, metastatic disease and hormone-refractory prostate cancer. PSMA is also present at high levels on the newly formed blood vessels, or neovasculature, needed for the growth and survival of many solid tumours. In contrast to other prostate-related antigens such as prostate-specific antigen (PSA), prostatic acid phosphatase (PAP) and prostate secretory protein, PSMA is a membrane glycoprotein that is not secreted. These unique attributes make PSMA an excellent target for monoclonal antibody diagnostic and therapeutic options in prostate and potentially other cancers.