Selective use of PET scan in the preoperative staging of NSCLC

Abstract

Positron emission tomography (PET) is a imaging technique which identifies abnormalities by utilising their metabolic properties rather than their anatomical density. In this study, we evaluated the place of PET scanning for the characterisation of additional abnormalities discovered on routine, preoperative CT evaluation of patients with proven NSCLC. A total of 21 patients underwent PET scanning using fluorodeoxyglucose (FDG). In these patients, routine CT scans had found 26 concomitant lesions which were in lung, adrenal gland, liver, kidney, spleen and pleura. FDG uptake was positive at the primary site in all patients. FDG uptake in 13 of the concomitant lesions suggested malignancy. Malignancy was confirmed at all of these foci by histology in eight (six at thoracotomy, fine needle aspiration biopsy (FNAB) and open biopsy) and by clinical and radiological follow-up for 1–15 months in five. In 13 lesions, PET suggested benign disease. Histology reported no evidence of malignancy in five and the six foci followed on clinical and radiographic follow-up for 2–16 months had no evidence of malignancy. PET was falsely negative in only one site where malignancy was proven by thoracotomy. PET failed to detect the remaining lesion which was an unassociated primary kidney tumour in a patient with Li-Fraumeni syndrome. The accuracy of PET scanning in the assessment of those additional lesions found on CT evaluation of otherwise operable NSCLC was found to be 96% with a sensitivity of 93% and specificity of 100%. These results indicate that PET is useful to characterise additional lesions found on CT scan of patients with NSCLC.

Introduction

The management of primary lung cancer depends on accurate staging. If disseminated disease is found surgery is generally contraindicated. Chest X-ray and CT scan are the imaging techniques routinely used for the preoperative evaluation of the patients with lung cancer, occasionally supplemented by magnetic resonance imaging (MRI). These examinations rely on size and density rather than the metabolic properties of the lesions. The sensitivity and specificity of these techniques is not ideal [1]. Invasive diagnostic techniques such as fine needle aspiration biopsy are frequently required before surgical therapy if a concomitant lesion is detected on CT scan. Despite thorough investigations, preoperative staging fails to identify metastatic deposits in a significant proportion of the patients who undergo thoracotomy [2].

In recent years, increasing interest has focused on positron emission tomography (PET), which identifies metabolically active foci, for the assessment of patients with lung cancer [3]. PET scan has been used clinically only in the last decade, although the principal mechanism on which it is based is an observation made in 1930 [4]. Warburg observed that cancer cells are characterised by higher glycolytic rate than normal cells. Deoxyglucose is a glucose analogue which is transported into cells by the same carrier proteins for glucose [5]. Deoxyglucose, like glucose, is phosphorylated by hexokinase to deoxyglucose-6-phosphate which does not proceed further in the metabolic pathway and remains metabolically trapped in the cell. Deoxyglucose is radiolabelled with the positron emitter 18-F. 18-F-fluoro-2-deoxy-d-glucose (FDG) is taken up by normal and malignant tissue and the amount of FDG which accumulates in the cell is proportional to the rate of glucose metabolism.

The first oncologic application of PET FDG was in brain tumours [6]. The technique was used not only for diagnosis but also for metabolic characterisation and assessment of prognosis of brain tumours [7]. Since Dahlbom and Hoffman developed a new acquisition and processing method for whole body PET scan [8], investigators have started to use this technique to investigate other tumours 9, 10, 11.

In lung cancer, the value of PET scan has been tested in different clinical conditions including the assessment of solitary pulmonary nodules, staging of primary disease, the detection of persistent or recurrent disease following treatment, and detection of unsuspected distant metastases 12, 13, 14. Early reports suggest that the technique has great potential on imaging and preoperative staging of lung cancer. This study focused on value of PET FDG for the assessment of the concomitant lesions found on CT scan in patients with NSCLC who were candidates for surgical treatment.