- Tracer shows promise for staging prostate cancer
Caren B. Les
Detecting cancer that is confined to the prostate bed, rather than after it metastasizes to the lymph nodes or skeletal system, is crucial for treatment and recovery. Although prostate cancer is the third leading cause of cancer death among American men, there is no highly reliable imaging technique for its detection, staging or restaging.
To address the clinical need for a better examination to stage this cancer, researchers conducted two translational studies on the use of the radiotracer anti-1-amino-3-18F-fluorocyclobutane-1-carboxylic acid (anti-18F-FACBC) in PET/CT imaging. The studies represent the move of the radioisotope tracer from in vitro studies to animal and human in vivo procedures.
Fused PET (left) and CT (center) anti-18F-FACBC images were taken of a 71-year-old male (restaging patient 1). Biopsy-proven recurrence of cancer in the prostate bed is shown by the arrow. The image to the far right demonstrates uptake of the probe in the prostate bed (arrow), but little bladder uptake (arrowhead). Reprinted with permission of the Journal of Nuclear Medicine.
After injection, the probe is drawn in higher concentrations to cancerous areas. PET reveals the metabolic signal of cancer cells, while CT generates an image of the anatomy, revealing the location, size and shape of abnormal growths. The results are fused to provide a single detailed image.
Headed by Dr. David M. Schuster, a pilot study on the use of the radioisotope tracer in humans was carried out at Emory University in Atlanta. Nine patients recently diagnosed with prostate cancer and six patients with a recurrence of the disease were injected with the radiotracer and then scanned using a GE Healthcare PET/CT scanner.
Visual analysis correctly identified the presence or absence of cancerous areas in 40 of 48 prostate image segments in eight patients with newly diagnosed disease. It correctly identified disease in four patients with proven recurrence (one prostate bed, three extraprostatic). The probe demonstrated low renal excretion or bladder activity, which is advantageous because imaging is hampered by the high radioactivity in urine.
Further study is needed to determine whether anti-18F-FACBC imaging can accurately distinquish cancer from areas of inflammation and hyperplasia. The most important finding of this initial study, according to Schuster, is that this technique detected metastatic prostate carcinoma. He said that a much larger study will be needed to further test the efficacy of the tracer.
In the study conducted at the Research Center of Nihon Medi-Physics Co. Ltd. in Chiba, Japan, scientists led by Shuntaro Oka evaluated anti-18F-FACBC in visualizing prostate cancer in animal models. The in vivo experiments were designed to determine the probe’s ability to differentiate between prostate cancer and inflammation and benign prostatic hyperplasia. Dynamic small-animal PET was performed on the abdomens of rats after the injection of anti-18F-FACBC or 18F-FDG, another tracer that has been used for diagnosing malignancies.
In comparison with the other probe, the anti-18F-FACBC tracer more accurately differentiated malignancy from benign lesions, according to Oka. It accumulated in high concentrations in the cancer cells and accumulated little in areas of inflammation and hyperplasia, and little was excreted into the urinary bladder.
Oka said that the next step in this area of research would be to address questions regarding the mechanism of anti-18F-FACBC uptake into the prostate cancer cells and of excretion into the urinary bladder. The researchers would like to address the relationship between the probe uptake level and tumor size, grade, PSA contents and/or type of prostate cancer. The feasibility of the probe for detecting other types of cancers is another area for exploration, he added.
Journal of Nuclear Medicine, January 2007, pp. 56-63; pp. 46-55.
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