NEW YORKAdvances in nuclear medicine may meet the need for more
accurate detection and higher-resolution imaging in breast and
prostate cancer management, especially in the assessment of bone
metastases, speakers said at a symposium on nuclear oncology
co-sponsored by Memorial Sloan-Kettering Cancer Center and Johns
Limitations of Current Prostate Cancer Imaging Techniques
One of the biggest challenges facing prostate cancer treatment is in
CT scans are not used routinely in prostate cancer and are of
Magnetic resonance images are reasonably accurate in detecting local
Conventional bone scans, he said, yield many false-positive results
Given the diagnostic limitations of the currently available imaging
The BSI Index
Steven M. Larson, MD, chief of nuclear medicine at Memorial
Sloan-Kettering, said that a newly derived bone scan index (BSI)
appears useful in predicting bone metastases in prostate cancer
patients whose PSA level changes may not accurately reflect their
outcomes. Defined as a quantitative estimate of the percent of total
skeleton invaded by metastases, the BSI has been shown to correlate
with survival time.
In a study of 191 patients with metastatic, hormone-refractory
prostate cancer, BSI values less than 4.1% equated with median
survival of 18.3 months, whereas BSI values greater than 5.1%
correlated with an 8.1 month median survival (P = .0079) (J Clin
Oncol 17:948, 1999).
The utility of the BSI resides in the rationale that cancer
treatment is predominantly guided by the stage and extent of the
tumor. Less cancer usually equates with a better overall response to
treatment, Dr. Larson said. Thus, any means available to more
accurately assess tumor burden in these advanced cancers could
markedly improve quality of life and possibly outcome, if treatment
is initiated early.
Such timely intervention is key, particularly since the progression
of bone involvement by prostate cancer is rapid. Dr. Larson reported
that initial BSI doubling times of about 43 days have been observed
prior to exponential rises in the index before leveling off. The
aggressive nature of such metastatic progression is illustrated in Figure
Dr. Larson also reported preliminary data on the use of positron
emission tomography (PET) scanning with 18F-fluorodeoxyglucose
(FDG) and 11C-methionine in a group of 10 prostate cancer
patients with high Gleason scores and rapidly increasing PSA levels.
Of 82 evaluable bone scan sites, 78% (64) were positive with FDG
imaging. Of 13 index lesions, 92% (12) were positive with 11C-methionine
These PET data are encouraging, but one must note that the
lesions studied were heterogeneous and these are advanced cancers.
However, the uptake of FDG through increased glycolysis in tumors,
and the uptake of labeled methio-nine through increased amino acid
transport, can provide information about clinically active sites in
bone and soft tissue, Dr. Larson explained. Importantly, these
data suggest that changes in tracer uptake levels may give early
evidence of a response to treatment.
Preliminary data for nuclear imaging of breast cancers also appear
promising. In a separate presentation, Dr. Larson described initial
data focusing on FDG-PET scanning and scintimammography with
technetium-99m (Tc 99m) sesta-mibi, a radiolabeled perfusion agent
originally indicated for cardiac imaging.
We have had most of our experience with advanced cancer
cases, Dr. Larson said, explaining that for these cases, the
focus has been on refining the differential diagnosis of bone
abnormalities, evaluating chest wall and brachial plexus involvement,
and, to some degree, looking at treatment responses.
A Recent Study
Dr. Larson said that in a recent study in 10 breast cancer patients
with clinical findings suggesting metastates, PET scanning correctly
identified metastatic tumors in 9 patients (90%). Moreover, FDG-PET
scans were used to confirm the presence of metastases following
inconclusive MR scans (Radiology 210:807, 1999).
FDG-PET scans are useful when intraosseous bone lesions require
evaluation to determine benign vs malignant tumors, Dr. Larson
said. He cited a case in which FDG-PET confirmed the absence of bone
metastases in a patient whose Tc 99m scan showed strong bony uptake
of the isotope, a finding that could imply malignancy (see
SUV Helps Interpretation
To better interpret FDG-PET scans, an index known as the
standardized uptake value, or SUV, is very helpful, Dr. Larson
said. This parameter gives an indication of whether malignancy is
present based on the degree of FDG uptake.
SUV ratios are calculated as the ratio of tumor-to-normal-tissue
uptake, measured as emitted photon counts and corrected for body
weight and injected dose. Normal bone-related SUV values are in the
range of about 1.6, whereas an SUV greater than 2 implies a better
than 90% chance of malignant bone involvement, he said.
Importantly, SUV data can correlate with treatment responses in
advanced cancer patients, Dr. Larson added, pointing out that
these ratios may reflect the metabolic activity of the tumor itself.