Improved technology allows for better prostate cancer staging

The use of capromab pendetide (ProstaScint, Cytogen, Princeton, NJ), a radiolabelled 7E11 antibody, has been controversial because of inconsistent imaging results. However, with improvements in imaging technology, the use of fused anatomic and functional images, and positive outcomes data, urologists can better determine the proper treatment protocol for intermediate- to high-risk patients and for those with rising PSA after radical prostatectomy using ProstaScint.

"You really need to think of ProstaScint as two different products," said Dr. Manyak, vice president of medical affairs at Cytogen and professor of urology, engineering, microbiology, and tropical medicine at The George Washington University in Washington. "The old ProstaScint used poorer quality gamma cameras, did not use fused images, and was more reliant on interpretation by nuclear medicine personnel. The new ProstaScint uses advanced state-of-the-art gamma cameras, fused images, and standardized software to provide much better anatomical detail."

"I believe that the sites that previously claimed it didn't work were just not getting good scans," Dr. Manyak said. "Now, everyone can get good scans with the improved gamma cameras and the use of co-registration to fuse images."

The radiolabelled antibody 7E11 is administered intravenously. The antibody binds to prostate-specific membrane antigen (PSMA). A gamma camera detects the antibody-radioisotope conjugate. When this image is fused with a CT or MRI scan, it clarifies, anatomically, the location of prostate cancer.

While PSMA is expressed in all forms of prostate tissue, it is upregulated in higher-grade prostate cancer, hormone-refractory cancer, and metastatic disease.An overexpression of PSMA has been shown to predict twice the rate of biochemical recurrence and a faster time to recurrence ( Clin Cancer Res 2003; 9:6357-62).

Another piece of the puzzle

"We are trying to improve our ability to stage prostate cancer, to image the disease, and to better define what the patient has before we treat them," said session moderator James A. Eastham, MD, associate professor of urology, Memorial Sloan-Kettering Cancer Center, New York. "Radioimmunoscintigraphy and fusion scans serve as another piece of the puzzle in trying to define the extent of disease and tailor therapy."

Outcomes data corroborate the value of this technology. Bruce Sodee, MD, and colleagues reported on 49 patients with fused images who underwent tissue biopsy ( Clin Prostate Cancer 2005; 3:230-8). Results showed the technology to have 83% accuracy in the detection of prostate cancer.

Michael Haseman, MD evaluated the ProstaScint uptake in the central abdominal region in 69 of 341 patients with a median follow-up of 4 years (RSNA 2003 scientific assembly, abstract 1076). Results showed that the presence of the signal in the abdomen correlated with a three-fold increase (p=.02) in prostate cancer-specific death, independent of the use or timing of androgen blockade and independent of PSA doubling time.

Rodney Ellis, MD reported 7-year data on fusion image-guided therapy with an altered dose of brachytherapy to areas of increased signal within the prostate (American Brachytherapy Society 2005 annual meeting, abstract 88). The results showed a highly statistically significant difference in biochemical disease-free survival for those patients with no signal outside the prostate, regardless of risk category (low, intermediate, or high) (p=.0004).