Imaging Tool Helps Locate Sites of Early Recurrent Prostate Cancer
DURHAM, N.C. -- A new multi-institutional study led by investigators at Duke University Medical Center indicates that a diagnostic scan may help localize recurrent prostate disease in men who have had surgical removal of the prostate and show early signs of recurrence.
This diagnostic scan, called capromab pendetide immunoscintigraphy, trade name ProstaScint®, is a monoclonal antibody scan that can detect recurrent disease if it is localized to the area of prior prostate surgery or has spread to other parts of the body. This knowledge can help doctors better decide which type of treatment would work best for each patient with recurrent prostate cancer. The study appears in the Feb. 15, 2002 issue of the journal Cancer.
Surgical removal of the prostate and surrounding lymph nodes — called radical prostatectomy — is an effective way to treat localized prostate cancer and stop the cancer's spread to other organs. If a man is cured with surgery, then his prostate specific antigen (PSA) level should be undetectable. However, according to the American Cancer Society, 40 percent of men have local recurrence of the disease after surgery, 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).
"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?' Identifying the location of recurrent disease is important because it can guide clinical management," said Dr. Ganesh Raj, of Duke's division of urology and lead author of the study. Localized recurrence may be treated with radiation therapy while distant disease is usually treated with hormonal therapy.
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. Both CT and bone scans are often only useful for localization of disease in patients with advanced disease.
"CT scans and bone scans will often come back negative in men with early signs of recurrent disease (low serum PSA)," said Dr. Thomas Polascik, of Duke's division of urology and the senior author on the study. "They may not be clinically useful in this situation."
However, 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.
The retrospective study examined a 75-center database comprising 265 prostate cancer patients who had undergone radical prostatectomies. Patients received no other treatment for their prostate cancer. Ten patients were excluded from the study because lymph nodes were not removed at the time of the prostatectomy.
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: One-hundred and nine 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 — for example, 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."
In addition, the researchers believe that studies with longer follow-up are 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 capromab pendetide immunoscintigraphy. Dr. Partin has served as a consultant to Cytogen, the manufacturer of the scan, in the past.