Involvement of mediastinal lymph nodes is a very important negative prognostic factor in
patients with non-small cell lung cancer (NSCLC). Moreover, in patients with N2 disease,
chemotherapy prior to surgery seems to increase the resectability and long-term survival.
Because of its low specificity and sensitivity, CT scan is not rewarding in staging of the
mediastinum and cervical mediastinoscopy remains the gold standard. Positron emission
tomography (PET) scan is able to collect biological information of tissue by the study of
glucose metabolism. PET scan has been found to be very accurate in the differentiation
between benign and malignant pulmonary nodules.
In this prospective study, we evaluated the value of PET scan in the staging of mediastinal
lymph nodes in patients with NSCLC. In 50 patients with potentially operable NSCLC
thoracic CT, PET scan and invasive surgical staging were performed. Surgical staging
consisted of mediastinoscopy and mediastinal lymph node dissection in case of operation.
Reading of the examinations was prospective and blinded to the pathological data. The
reading of the PET scan was visually correlated with CT scan to get a better differentiation
between the hilum and mediastinum.
In 15 patients, mediastinal nodes were suspect on PET scan. This was correct in 14 patients,
in one patient it was false positive (positive predictive value: 93%). In 35 patients, the
nodes were not suspect on PET scan. In all these patients, mediastinoscopy was negative
and intraoperative staging showed microscopic metastatic disease in mediastinal nodes in
only one patient (negative predictive value: 97%).
We conclude that the NPV of PET scan is very high (much higher than the NPV of CT scan
and even higher than the NPV of cervical mediastinoscopy!!). Because of the high NPV, PET
scan becomes a very important staging method in patients with NSCLC and this could
reduce the need for invasive staging of the mediastinum very remarkably.