PET Shows Promise in Screening for Axillary Node Metastases

February 1, 1997

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.

CHICAGO--Positron emission tomography (PET) has excellent potentialas a screening test for spotting axillary lymph node metastases in womenwith newly diagnosed, early-stage breast cancer, thereby sparing many womenfrom unnecessary lymph node dissection, Lee Adler, MD, of Case WesternReserve University, said at the Radiological Society of North America meeting.

In his study, PET scans of the axilla that measured uptake of fluorine-18deoxyglucose (FDG), a radioactive tracer that illuminates regional glucoseutilization, identified nearly all women with positive lymph nodes.

Based on his analysis of 56 women, Dr. Adler believes that "a negativePET scan is strong evidence against the presence of axillary metastases."After categorizing all definitive, probable, and equivocal emission scansas positive, he found that FDG PET had a sensitivity and a negative predictivevalue of 95%.

Specificity May Be Sacrificed

Because the degree of uptake of FDG at times appeared to be the samewhether or not a woman had metastases in the axillary lymph nodes, Dr.Adler acknowledged that specificity may be sacrificed in order to assurehigh sensitivity.

As one example, he pointed to a small focus of moderately increasedtracer accumulation that was found in one women with metastatic breastcancer and a nearly identical focus of tracer accumulation seen in anotherwoman who had a negative lymph node dissection. If foci with moderate traceruptake are classified as positive in order to assure high sensitivity,"we're going to have to call these other foci positive as well, andwe'll lose specificity," he said.

Despite a specificity and positive predictive value of only 62% andan overall accuracy rate of 75%, Dr. Adler believes that FDG PET is a promisingscreening tool for women with newly diagnosed breast cancer. "Onemight at first be disappointed by the relatively low specificity and overallaccuracy values," he said. "But remember," he added, "weare talking about using PET as a screening test rather than a diagnostictest. What's most important for a screening test is a high sensitivityand an acceptable specificity, which I believe we have."

Another factor is the cost that may be saved by preventing unnecessarysurgical dissection. If the lymph node dissection had not been performedin the 22 patients who had negative scans, Dr. Adler determined that FDGPET would have saved $180,000 in surgical costs. After subtracting thecost of performing FDG PET on all 56 patients, he calculated a total netsavings of $2,000.

"The strategy of avoiding axillary lymph node dissection in thepatients with negative PET tests would have prevented nearly two thirdsof the negative lymph node dissections that were performed in our studygroup," he concluded.