CHICAGO--Positron emission tomography (PET) has excellent potential
as a screening test for spotting axillary lymph node metastases in women
with newly diagnosed, early-stage breast cancer, thereby sparing many women
from unnecessary lymph node dissection, Lee Adler, MD, of Case Western
Reserve University, said at the Radiological Society of North America meeting.
In his study, PET scans of the axilla that measured uptake of fluorine-18
deoxyglucose (FDG), a radioactive tracer that illuminates regional glucose
utilization, identified nearly all women with positive lymph nodes.
Based on his analysis of 56 women, Dr. Adler believes that "a negative
PET scan is strong evidence against the presence of axillary metastases."
After categorizing all definitive, probable, and equivocal emission scans
as positive, he found that FDG PET had a sensitivity and a negative predictive
value of 95%.
Specificity May Be Sacrificed
Because the degree of uptake of FDG at times appeared to be the same
whether or not a woman had metastases in the axillary lymph nodes, Dr.
Adler acknowledged that specificity may be sacrificed in order to assure
As one example, he pointed to a small focus of moderately increased
tracer accumulation that was found in one women with metastatic breast
cancer and a nearly identical focus of tracer accumulation seen in another
woman who had a negative lymph node dissection. If foci with moderate tracer
uptake are classified as positive in order to assure high sensitivity,
"we're going to have to call these other foci positive as well, and
we'll lose specificity," he said.
Despite a specificity and positive predictive value of only 62% and
an overall accuracy rate of 75%, Dr. Adler believes that FDG PET is a promising
screening tool for women with newly diagnosed breast cancer. "One
might at first be disappointed by the relatively low specificity and overall
accuracy values," he said. "But remember," he added, "we
are talking about using PET as a screening test rather than a diagnostic
test. What's most important for a screening test is a high sensitivity
and an acceptable specificity, which I believe we have."
Another factor is the cost that may be saved by preventing unnecessary
surgical dissection. If the lymph node dissection had not been performed
in the 22 patients who had negative scans, Dr. Adler determined that FDG
PET would have saved $180,000 in surgical costs. After subtracting the
cost of performing FDG PET on all 56 patients, he calculated a total net
savings of $2,000.
"The strategy of avoiding axillary lymph node dissection in the
patients with negative PET tests would have prevented nearly two thirds
of the negative lymph node dissections that were performed in our study
group," he concluded.