The test, which combines monoclonal antibody with radiation and large x-ray scan, can both show early signs of recurrence and where the recurrence has spread within the body.

The multi-institutional study led by Dr. Ganesh Raj at Duke University Medical Center appears in the Feb. 15, 2002 issue of the journal Cancer.

"When we see a rise of the PSA level in a man who has already had his prostate removed, the first question for the physician is, ‘Where is the recurrent cancer? Has the disease remained localized or has it spread to other parts of the body?'” Raj said in a press release.

“Identifying the location of recurrent disease is important because it can guide clinical management. Localized recurrence may be treated with radiation therapy while distant disease is usually treated with hormonal therapy." said Raj,

This diagnostic scan, called capromab pendetide immunoscintigraphy, trade name ProstaScint®, uses a monoclonal antibody designed to find and attach itself to prostate cancer cells. The antibody is combined with a radioactive tracer, indium 111, to form a drug that is injected into a patient. After four days, the patient's body is scanned. Lymph nodes that have been invaded by prostate cancer cells appear as "hot spots" on the test.

The study examined a 75-center database containing medical information about 255 prostate cancer patients who had undergone radical prostatectomies. Patients received no other treatment for their prostate cancer.

All but three of the 255 men in the study showed an elevation of PSA levels, the only sign that their cancer might be returning. Recurrent disease was detected by the capromab pendetide scan in 184 of the men (72 percent). Furthermore, in these patients, the scan showed the extent of the disease: 109 men (59 percent) had disease confined either to the prostatic bed or the local lymph nodes, while 75 (41 percent) had disease that had spread into distant lymph nodes and or bone.

Comparisons to other imaging techniques showed that only 11 percent of this group had recurrent disease detected by a bone scan and only 16 percent had recurrence detected by CT scan. These data indicate that the capromab pendetide scan may be more sensitive than the bone or CT scans in identifying the site and extent of disease recurrence in patients with low PSA levels.

"This data is encouraging and shows the clinical utility of the capromab pendetide scan," said Dr. Raj. "A major limitation of this study is the fact that we don't have any histological evidence -- no tissue samples of the suspected area of disease -- to confirm the scan's results. However, previous studies have shown that a positive scan correlates well with histologic evidence of metastatic prostate cancer."

According to the American Cancer Society, 40 percent of men treated with surgical removal of the prostate have local recurrence of the disease, and 11 percent are at high-risk of the recurrent disease spreading to other organs. Often, the first sign of recurrent prostate cancer after surgery is an elevated PSA level. The recurrent disease may remain in the local area of the excised prostate (localized recurrence), or may spread into distant lymph nodes or other tissues (distant recurrence).

Currently, when a patient has an elevated PSA level after prostatectomy, he may undergo a computed tomography (CT) scan or bone scan. But CT scans, which X-ray organs of the body, cannot pick up tumor deposits if they are less than 10 to 15 millimeters in size, and bone scans, which take two-dimensional images of the bone, can only pick up a significant burden of tumor cells that have spread into the bones.

The capromab pendetide scan can detect lesions as small as 5 millimeters and has been shown in earlier studies to detect metastatic prostate disease in men with high PSA levels. However, no prior study had examined its capabilities in evaluating men with mildly elevated PSA levels often indicating early recurrence of cancer.

More research with longer follow-up is needed to determine the true clinical utility of capromab pendetide immunoscintigraphy and its impact on clinical outcomes.

Dr. Alan W. Partin, of the Brady Urological Institutes, The Johns Hopkins Medical Institutions, also was a co-author on the study. Drs. Raj, Polascik and Partin have no financial interest in the technology, although Partin served in the past as a consultant to Cytogen, the manufacturer of the scan.

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