"This new test, called ProstaScint, fills a void," says Salma Khan, M.D. a nuclear medicine specialist at the University of Maryland Medical Center, where the test has been performed on 18 patients. "It gives us more information and helps us to determine the best course of therapy for each patient," says Dr. Khan, who is also an assistant professor of radiology at the University of Maryland School of Medicine.
The test uses a monoclonal antibody designed to find and attach itself to the wall of 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. Through this analysis, doctors can determine whether the cancer has remained local, within the prostate, or if it has spread to lymph nodes anywhere in the body. It can find tumors within lymph nodes as small as a quarter of an inch in length.
The ProstaScint is useful in patients with newly diagnosed prostate cancer to help decide if they should have surgery to remove the prostate. The test also helps post-surgical patients with rising blood levels of prostate specific antigen (PSA), to determine where the cancer may have spread. Before this test was available, patients received a CT scan. That test only detects enlarged lymph nodes once they reach about one-third of an inch in size, and does not reveal whether the nodes are enlarged because of cancer.
"This new test will help us determine which patients should undergo surgery," says Stephen Jacobs, M.D., professor of surgery and head of urology at the University of Maryland Medical Center. "If the cancer has spread, surgical removal of the prostate would not cure the disease. Patients whose cancer has spread outside the prostate gland may benefit from radiation therapy. And if cancer is evident in the lymph nodes outside of the pelvis, hormonal therapy may be the best treatment," says Dr. Jacobs, who is also co-director of the Urologic Oncology Program at the University of Maryland's Greenebaum Cancer Center.
According to the American Cancer Society, about 317,000 men in the U.S. were diagnosed with prostate cancer in 1996. It is the most common type of cancer in men.
The test was approved by the FDA in late 1996. Since then, selected sites around the country, including the University of Maryland Medical Center, have been performing ProstaScint. Each hospital must go through an accreditation process prior to becoming certified to perform the exam.
Other antibody tracer exams are currently used for diagnosis of colorectal, lung, and ovarian cancer. Studies are underway to evaluate use of antibody tracer tests for patients with breast cancer and lymphoma.
The University of Maryland's Greenebaum Cancer Center provides a full spectrum of diagnosis and treatment options for patients with prostate and other urologic cancers.