The emergence of radioimmunoscintigraphy for prostate cancer

Abstract

The ability to label tissue-specific antibodies has long been of interest for improving detection and guidance for therapeutic applications. The most studied target for prostate cancer is the prostate-specific membrane antigen, which is upregulated in prostate cancer, hormone-refractive disease, and prostate cancer metastases. Investigations using radioimmunoscintigraphy with the radiolabeled 7E11 antibody capromab pendetide have significantly improved sensitivity for prostate cancer detection compared with standard cross-sectional imaging, based on tissue confirmation of pathologic results. Over the past 5 years, significantly greater image resolution from improved camera technology and the use of co-registration to fuse functional and anatomic (computerized tomography and magnetic resonance imaging) images have dramatically enhanced prostate cancer localization. Outcomes data from several sources have spurred a resurgence in interest in this imaging modality.

Figure 1

Physiologic, anatomic, and fused images, showing a suggestion of increased activity on the ProstaScint (physiologic) scan (A) and very small periprostatic (PPFLN) and perirectal (PRLN) lymph nodes that do not meet the size criteria for malignancy on the computerized tomography (anatomic) scan (B). C. The fused image demonstrates increased signal intensity in lymph node structures separate from vascular structures and bone marrow. Note the signal in the blood pool of the male genital system external to the body and in the spermatic cord (SC). FV, femoral vein; R, rectum; P, prostate; AM, acetabular marrow; SM, symphysis pubis; IM, iliac marrow. Courtesy of Michael K. Haseman, MD, Sacramento, CA.

Figure 2

Schematic depiction of the most common areas of pelvic lymph node metastasis from prostate cancer.

Figure 3

Physiologic, anatomic, and fused images in transaxial (top row), coronal (middle row), and sagittal (bottom row) planes. All image sets are triangulated on the obturator node (ON) seen on the ProstaScint (physiologic) scan (images on the left). Lymph nodes not clearly seen on the computerized tomography (anatomic) scan (images in the middle) are designated as obturator node region (ONr). Note the benign uptake in the degenerative lumbar spine (LSp), acetabular marrow (AM), bladder (B), femoral veins (FV), femoral marrow (FM), iliac marrow (IM), and rectum (R). CIV, common iliac vein; SaM, sacral marrow. Courtesy of Leone Gordon, MD, Medical University of South Carolina, Charleston, SC.

Figure 4

Fused ProstaScint and MRI images (right) demonstrating 2 areas of focal activity (white arrows) that correspond to step-sectioned pathologic presence of prostate cancer (black arrows, left). Circled areas without arrows represent inflammation. Courtesy of Rodney Ellis, MD, and Bruce Sodee, Case Western Reserve University, Cleveland, OH.

Figure 5

A. Periaortic lymph node (PAN) and bowel (Bo) activity detected on radioimmunoscintigraphy. Small periaortic lymph nodes are noted on computerized tomography (B), with confirmed high-signal activity on the fused scan (C) separate from intestinal excretion. A, aorta; IVC, inferior vena cava. Courtesy of Robert McDonald, MD, Fort Myers, FL.

Figure 6

A. Increased signal intensity (arrow) on fused ProstaScint scan in the prostatic bed of a patient with a rising prostate-specific antigen (PSA) level after PSA nadir at undetectable levels following radical prostatectomy. Note the mild activity in the bowel and bone marrow. B. Repeat fused ProstaScint scan in the same patient 6 months after salvage external beam radiotherapy, with now undetectable PSA. The absence of signal in the prostatic bed contrasts with the presence of increased signal in the rectal lumen and bowel. Without scan fusion to align anatomy with the functional study, this scan would have been falsely read as persistently positive. Both images courtesy of Bradley Prestidge, MD, and Yong Bradley, MD, Texas Cancer Clinic, San Antonio, TX