Human trial of anti-F-18 FACBC tracer shows promise for prostate cancer

CONTEXT: While prostate-specific antigen testing and biopsy are the most conclusive ways for detecting prostate cancer, no clear-cut imaging technique exists for initial diagnosis and staging. A preliminary study led by Dr. David Schuster, director of nuclear medicine and molecular imaging at Emory University, analyzed the PET agent anti-fluorine-18 FACBC for these roles. The amino acid-based radiotracer (a synthetic L-leucine analog) is designed to have properties of optimal nonspecific binding and metabolism. Compared with FDG, which does not accumulate in prostate tumors, anti-F-18 FACBC shows little renal excretion.

RESULTS: Following an injection of anti-F-18 FACBC, nine patients with newly diagnosed prostate cancer were scanned with PET/CT. Subjects underwent 65 minutes of dynamic imaging of the pelvis followed by static whole-body imaging. Maximum standard uptake value, recorded in the right and left lobes of the prostate and within lymph nodes, peaked within six minutes after infusion and remained significantly higher for at least 50 minutes in primary and metastatic prostate carcinoma compared with benign regions in 14 of 16 lobes. Malignant sextants and nodes had significantly higher SUVmax than did benign regions, though the numbers in this pilot study were small.

Visual analysis often successfully identified the presence or absence of neoplasia. Four false positives associated with inflammation and four false negatives stemming from microscopic disease arose from interpretation of delayed images. Uptake was elevated for recurrent disease in the prostate bed, and associated nodal and skeletal metastases often appeared when indium-111 ProstaScint uptake was not evident.

IMAGE: Intense FACBC uptake, indicative of recurrent cancer, appears in small right common iliac nodes (left). Corresponding ProstaScint SPECT image of the same patient was negative for iliac lymph node involvement.

IMPLICATIONS: Pilot data suggest anti-F-18 FACBC will be an effective agent for imaging early prostate cancer compared with FDG-PET/CT or In-111 ProstaScint. Lymph imaging indicates it could help differentiate between prostatic and extraprostatic reccurrence, Schuster said. Following on these positive yet limited results, subsequent trials will examine more patients to develop a strategy for clinical imaging.