‘Hottest’ Sentinel Lymph Nodes Not Necessarily the Likeliest to Contain Metastasis

WASHINGTON—Although locating sentinel lymph nodes (SLNs) for biopsy often depends on radioisotope mapping, the node with the highest isotope uptake is not necessarily the one likeliest to contain metastasis, said Robert C. G. Martin, MD, of Memorial Sloan-Kettering Cancer Center.

In a group of breast cancer patients known to have axillary node metastases, the "hottest" node tested negative 20% of the time, Dr. Martin said at the 54th Annual Cancer Symposium of the Society of Surgical Oncology. The presence of blue dye in itself proved no more reliable in indicating which node would be positive, he added.

Sentinel lymph node biopsy is becoming "the new standard of care for early breast cancer axillary node staging," Dr. Martin said, but he added that no standard technique now exists nor any standard definition of what constitutes a sentinel node that should be excised.

"The blue node definition is unambiguous," he stated, but radioisotope definitions vary. The University of Louisville "10% rule," for example, defines a sentinel node as any with an isotope count within 10% of the "hottest" node found.

But, Dr. Martin asked, is there only one true sentinel node? Or do individuals often have more than one? He reported on a study of 2,289 patients with stage I-II breast cancer that aimed to find out.

Each patient underwent SLN biopsy using both blue dye and radioisotope mapping. Isotope localization was considered successful when the ex vivo ratio of isotope in the sentinel lymph node to that in the axillary background reached 4:1 or higher.

All nodes located in this manner were removed and submitted for pathologic analysis that included both serial sections and immunohistochemistry.

Multiple sentinel nodes were found in 1,566 of the patients, 30% of whom had nodes containing metastases. In 20% of these cases, or 94 individuals, however, the node showing the highest isotope count was benign and a node with a lower isotope count proved malignant.

In 48 of these patients (51%), the radiologically "hottest" benign node was more than five times "hotter" than a positive node. Blue dye also missed positive nodes in 27% of the patients with known metastases.

Removing only the radiologically "hottest" node would have produced an unacceptably high false-negative rate, Dr. Martin observed. Removing all nodes containing isotope, as well as all with blue dye, yielded a 4% false-negative rate, however, he said.

Accuracy therefore requires that surgeons remove all nodes that contain isotope, rather than only those with the highest counts, Dr. Martin concluded.