PET Scans and Lung Cancer
ABSTRACT & COMMENTARY
Synopsis: PET scans may be helpful in the preoperative evaluation of the mediastinum in patients with lung cancer. Because of the high specificity, it may be possible to omit a staging procedure when the medistinal nodes are negative on the PET scan. Although the positive predictive value of PET scans is high, a medistinal staging procedure was still recommended. PET scans are also helpful in the evaluation of distant metastatic disease. In the study by Weng et al, the PET scan changed the management in 24% of the cases.
Source: Weng E, et al. Am J Clin Oncol 2000;23:47-52.
The purpose of this study was to evaluate the use of computerized tomography (CT) and positron emission tomography (PET) scans in staging lung cancer patients. Using pathological confirmation, the sensitivity, specificity, and accuracy of staging nodal disease could be calculated. The effect on clinical management was assessed and recommendations for the use of PET scanning in lung cancer were made.
The study involved a retrospective review of 50 consecutive lung cancer patients from 1992 to 1997. The patients were felt to have resectable disease and underwent CT scans, PET scans, and surgical staging. Three patients with small-cell lung cancer were included along with the 47 non-small-cell lung cancer patients. The CT scan covered the supraclavicular region to the adrenal glands; the article does not explicitly state whether the brain was routinely imaged by CT scanning in every patient. However, the PET scan included both the head and the body.
The PET scan was superior to the CT scan in terms of specificity (PET scan = 94%, CT scan = 77%, P = 0.025). Together, the PET scan and CT scan had a specificity of 96%. Because of these results, Weng and associates recommend that a mediastinal staging procedure is not needed before definitive surgery if both the PET scan and CT scan of the mediastinum are negative. In fact, Weng et al also believe that a mediastinoscopy can be omitted after a negative PET scan even if the CT is positive, particularly with T1 or T2 tumors. For example, of nine patients with N2 disease by CT scan but N0 or N1disease by PET scan, the PET scan concurred with the biopsy in each case.
PET scans and CT scans were found to be equally sensitive at 73%. The positive predictive value of the PET scan (true positive result divided by all positive results) was 85%. This improved to 90% if both the PET scan and the CT scan were used. Nevertheless, one would not want to miss those potentially curable patients who despite (false) positive PET scan results had pathologically negative mediastinal nodes. Therefore, Weng et al recommend that a patient with a positive PET scan for N2 disease (whether the CT is positive or negative) should still undergo a mediastinal staging procedure.
In this study, the PET scan also influenced the treatment decisions because of findings outside of the chest. Two patients with possible solitary metastatic disease by CT scanning went on to have biopsies because the PET scan was negative. These two lesions were shown to be an acoustic neuroma and a liver hemangioma. Another patient was found to have stage IV disease after the PET scan found a brain metastasis that was missed by CT.
COMMENT by Kenneth W. Kotz, MD
As PET scanners become more widely available in the United States, oncologists will need to become familiar with this new modality. Indeed, the last two ASCO Educational Books have included sections on PET scans.1,2 The potential power of PET scans is demonstrated in the lung cancer study by Weng et al, where the results of the PET scan changed management decisions in 24% of the cases.
Weng et al found that the most accurate analysis of the mediastinum was when the results of the CT and PET scans were correlated. This suggests that these two imaging modalities are complementary. Because detection of malignant N2 nodes has important treatment implications in non-small-cell lung cancer, at least 15 studies have looked at the role of PET scans in the preoperative evaluation of these patients.1 In these studies, the specificity of PET scanning seemed to be around 91% (range, 81-100%) with a sensitivity of around 88% (range, 78-100%).1 A meta-analysis including 14 studies comparing PET and CT scans for detection of N2 disease has been published.3 In this analysis, the specificity of PET scans was 91% (compared with 77% for CT scans) and the sensitivity of PET scans was 79% (compared with 60% for CT scans). The specificity from these studies is comparable to what is being reported by Weng et al. However, the sensitivity of 73% reported by Weng et al is slightly lower than has been generally reported.
Weng et al recommend omitting a pre operative mediastinal staging procedure if the PET scan is negative for mediastinal involvement. This approach has been advocated by others.2,4 In addition, Weng et al also recommend proceeding with a mediastinal staging procedure even when the PET scan is positive. This approach has also been advocated by others2,4 and is important because potentially curable patients will not be inappropriately upstaged. Despite the high positive predictive value of a PET scan, false positive results can be seen when it is difficult to distinguish N1 from N2 nodes, or in the presence of active inflammatory conditions. The study by Weng et al adds to the growing list of studies demonstrating the usefulness of PET scanning in the staging and pre operative evaluation of non-small cell lung cancer patients.
References
1. Hoffman J. ASCO Educational Book 2000:162-168.
2. Wahl R, et al. ASCO Educational Book 1999:604-613.
3. Dwamena BA, et al. Radiology 1999;213:530-536.
4. Wahl R. PPO Updates 1997:1-24.
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