The blood level of the enzyme aspartyl beta-hydroxylase may be a more sensitive and specific biomarker for early prostate cancer than prostate-specific antigen or digital rectal exam, according to a presentation at the first meeting on Molecular Diagnostics in Cancer Therapeutic Development, organized by the American Association for Cancer Research.

The need for better testing is highlighted by the discrepancies often found between the two current, commonly used screens, digital rectal examination and blood prostate-specific antigen level. A man who has prostate cancer can have both a normal results with both tests, and, conversely, an individual with a high antigen level and an abnormal rectal examination could be cancer-free.

Stephen Keith, MD, president and chief operating officer of Panacea Pharmaceuticals, Inc., which conducted the new enzyme testing, said “Currently, if an individual has a high prostate-specific antigen and positive digital rectal examination, the recommendation is that he has a biopsy of the prostate, and more often than not ? by some estimates, as much as 80 percent of the time ? there will not be evidence of cancer.”

Hossein Ghanbari, PhD, said that earlier studies have shown that aspartyl beta-hydroxylase is over-expressed in at least 20 types of cancer, including liver, breast, ovarian, colon, esophageal, and prostate. It has been shown to be involved in tumor growth, invasiveness, and metastasis.

The researchers previously examined tissue from more than 20 different cancer types and compared them with more than 1,000 normal tissue types. Using immunohistochemistry techniques, they found that more than 99 percent of cancers were positive for the enzyme, but none of the normal issue samples was positive.

In the current work, researchers compared blood enzyme levels of 16 patients with prostate cancer with levels of 23 healthy men. Patients with prostate cancer had high enzyme levels, whereas none of the normal control men did.

The authors hope addition of enzyme testing to the current screening standards can better identify men who should undergo prostate biopsy. Clinical trials are planned that will evaluate prostate tissue samples from 800 patients, 400 men with prostate cancer and 400 healthy men.