PET Scans Spare Some NSCLC Patients From Mediastinoscopy

NEW ORLEANS—The high negative predictive value of positron emission tomography (PET) imaging can spare some patients with early non-small-cell lung cancer (NSCLC) the need for mediastinoscopy prior to thoracotomy,

Michael P. Farrell, MD, said at the American Roentgen Ray Society annual meeting. Dr. Farrell and his colleagues from the Department of Radiology, Duke University Medical Center, have demonstrated that fluorodeoxyglucose (FDG)-PET imaging can detect micrometastases that computed tomography (CT) may miss.

Disease stage at presentation dictates the management of NSCLC. Although stage I-IIIa NSCLC is considered to be potentially operable, about 20% to 30% of patients with no evidence of lymph node involvement or widespread metastases on CT nonetheless have mediastinal lymph node metastases. CT is suboptimal because it can fail to detect micrometastases in normal-sized nodes.

At many institutions, stage I patients are referred for mediastinoscopy prior to thoracotomy. “Mediastinoscopy,” Dr. Farrell noted, “is stressful and requires general anesthesia. In addition, sampling techniques are variable.” Since the sensitivity of CT is only 60% for identifying nodal metastases, Dr. Farrell and his colleagues asked whether FDG-PET imaging, a noninvasive method, could distinguish those patients who require nodal sampling from those who should go immediately to thoracotomy.

FDG-PET images from 96 patients were retrospectively reviewed: 70 had nodal sampling at thoracotomy, and 20 had undergone mediastinoscopy. The remaining 6 patients were referred for radiotherapy due to poor respiratory function and were excluded from the study.

The FDG-PET technique correctly staged 82% of the cases, overstaged 12%, and understaged 5%. The sensitivity of FDG-PET was 0.56 for detecting involved hilar lymph nodes, and the specificity was 0.95. Although the sensitivity for hilar nodes is relatively low, he said, this doesn’t alter management because these patients go directly to thoracotomy regardless.

For mediastinal nodes, FDG-PET had a sensitivity of 0.8 and a specificity of 0.92, with a positive predictive value of 0.36 and a negative predictive value of 0.99. “With such a high negative predictive value, stage I NSCLC patients with a negative FDG-PET scan can proceed directly to thoracotomy,” Dr. Farrell said. Those with positive scans should still undergo mediastinoscopy; the FDG-PET images can be used to target lesions to be biopsied by the surgeon.

“There remains no consistent workup for staging early NSCLC, and this study may prove helpful for many patients,” said Ned Patz, MD, professor of radiology, Duke University Medical Center, and a collaborator on the study.