Sentinel Lymph Node Mapping Studied in Lung Cancer

CHICAGO—Intraoperative sentinel lymph node mapping using technetium-99 sulfur colloid is a safe and feasible way of identifying sites of lymph node metastasis in patients with non-small-cell lung cancer (NSCLC). The procedure does not prolong surgical resection, and it is relatively accurate, with an 89% success rate, Michael Liptay, MD, reported at the Second International Chicago Symposium on Malignancies of the Chest and Head & Neck.

"Sentinel lymph node mapping in lung cancer may allow pathologists to provide more precise nodal staging information on the presence of micrometastatic disease," said Dr. Liptay, assistant professor of thoracic surgery, Northwestern University School of Medicine, Evanston, Illinois.

Dr. Liptay and his colleagues at Northwestern have been assessing sentinel lymph node mapping in lung cancer patients for the last 2 years to determine if it would improve staging.

Sentinel lymph node mapping is used in patients with breast cancer or melanoma to limit potentially morbid and nontherapeutic nodal dissection. In the lung, it may prove to be a sensitive pathologic technique for assessing selected lymph nodes rather than the entire surgical specimen, he said.

Although lymph node involvement is the strongest predictor of survival for patients with localized lung malignancies, nearly 40% of patients who appear to have node-negative disease at pathologic analysis relapse within 2 years of resection, Dr. Liptay noted. "It is our hypothesis that undetected and occult metastases in the lymph nodes may explain some of these early relapses," he said.

In Dr. Liptay’s study of 91 patients, 0.5 to 2.0 mCi of radioactive technetium 99 sulfur colloid was injected directly into the tumor in a four-quadrant pattern immediately following thoracotomy.

After 10 minutes of surgical dissection of lung tissue away from the lymphatics in the peribronchial area, a hand-held gamma camera was used to obtain readings of the primary tumor and lymph nodes. Lymph nodes identified as the first nodal draining sites of solid lung tumors were examined in ten 20-µm serial sections, and all dissected lymph nodes underwent antibody staining.

All 91 patients had complete resection of their lung cancer. Sentinel lymph nodes were identified in 78 patients (86%), and 69 of these sentinel nodes (88.5%) were classified as true positive. Metastases in other intrathoracic lymph nodes were found only when sentinel lymph nodes were involved.

The sentinel node was the only positive node in 9 of 21 patients (42%), and the sentinel node was shown to contain micrometastatic disease in serial sections and antibody staining in biopsy specimens from 7 patients (31%). As a result, 9% of patients in this series were upstaged on the basis of sentinel node mapping. "We also noted about a 20% incidence of skipped metastatic pattern, where the sentinel node was in the mediastinum," Dr. Liptay said.

He concluded that sentinel node mapping in the future may help surgeons perform more complete nodal dissection in patients with NSCLC.