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J Thorac Cardiovasc Surg 2003;126:15-16
© 2003 The American Association for Thoracic Surgery
General thoracic surgery |
Dr David J. Sugarbaker (Boston, Mass). I very much appreciated the opportunity to read the article by Dr Flores and his group at Memorial regarding this interesting study of PET and mesothelioma. I think it is important to look for different modalities to understand preoperatively the extent of disease in mesothelioma, and I suggest that the findings in this particular study are not unexpected. The difficulty of defining the preoperative stage in mesothelioma is derived from the fact that the geographical distribution of the tumor, unlike other malignancies, is very diffuse, and all of the modalities, including MRI and CT scan (which preceded PET), have had difficulty in defining preoperatively the appropriate stage. Nevertheless, this study suggests that there are some limited useful applications of PET in mesothelioma, particularly in those malignancies that have a high metabolic rate taking up a lot of the markers; thus, there is the implication of a very high mitotic index and therefore a higher propensity to spread to the lymph nodes. Unfortunately, there is a very small group of patients who will demonstrate distant metastatic disease at the time of presentation. Nevertheless, in this small group of patients, it seems that PET has some usefulness.
I have 3 questions for Dr Flores and his group at Memorial, who obviously have extensive experience with mesothelioma. First, I believe 21 patients in your series were "open and close," unresectable. Given the limited cohort you had, this seems to be a relatively high unresectability rate. Would you address that and tell us if there was anything in the MRI, CT, or other aspects of the preoperative workup that may have indicated that these patients were indeed unresectable before their exploration? As a sideline to that question, was there a propensity for these patients to be mixed or sarcomatous types as opposed to epithelial types?
My second question concerns your statement that MRI is unreliable in determining resectability. Some years ago at Brigham, I, Dr Patz, and some of our colleagues in radiology wrote about the fact that although MRI is somewhat limited, it is the most useful preoperative staging radiologic modality when coupled with echocardiography. This is primarily because MRI allows one to see 2 important areas more easily and accurately than CT scanning: transdiaphragmatic extension of the disease and transmediastinal invasion into structures that are clearly going to render the patient unresectable. So, I ask you to comment on your use of MRI and echocardiography at Memorial in the workup of these patients.
Third, would you comment on the presence or absence of chest pain in your patients who are unresectable? What is your use of mediastinoscopy in the preoperative workup of these patients? We have found that even mild chest pain is often the best predictor of diffuse chest wall invasion by these tumors.
I thank Dr Flores and his group and congratulate them on an excellent study, which I think contributes to our knowledge of mesothelioma and to our understanding of the use of PET scanning in this disease.
Dr Flores. I will start by combining the first and third questions. In regard to the unresectability rate, many PET scans performed in patients were not obtained uniformly. Initially, more PET scans were performed in patients who had a higher tumor bulk on CT; thus, theoretically, they may have had a higher incidence of unresectability. This was an inhomogeneous group of patients. Not every single patient underwent PET scanning, and I do have to say that the study was biased toward the patients who had a higher indication of unresectability on CAT scan.
When patients experienced chest pain, it indicated the necessity for a PET scan; however, the scan was not uniformly obtained by every surgeon. But, those patients who experienced chest pain did tend to have PET scans performed.
Two patients with sarcoma in this series were found to have T4 lesions. In regard to MRI, I am very aware of the article written by you and your colleagues demonstrating the usefulness of MRI. There was also another article written by investigators at our institution (Dr Hellan was the first author) that basically compared MRI and CT scan, and although MRI did have a higher rate of diagnosing (eg, as you stated, transdiaphragmatic invasion), this was not found to be a clinically significant finding as far as changing the preoperative management of the patient. Thus, although MRI may be sensitive in certain areas, it does not change the decision to take the patient to the OR.
Our experience at Memorial demonstrates that echocardiography is not helpful in these patients, and we usually obtain cardiac sestamibi stress tests instead. Because of the magnitude of the operation, we look more for cardiovascular disease rather than pericardial effusions. We do not routinely perform mediastinoscopy, but I do think that needs to be studied.
Dr D. Miller (Atlanta, Ga). I would echo your thoughts. In regard to PET, it is not very accurate within the mediastinum, but it has helped tremendously for distant metastasis. At the Mayo Clinic, we routinely proceed with a mediastinoscopy before an extrapleural pneumonectomy. However, in several operations, performed after a preoperative PET scan that showed no nodal involvement, on entering the chest, we found N2 nodal involvement at the paraesophageal or the inferior pulmonary ligament nodes, which correlates more with lower chest disease. Where were the N2 nodes located in your 8 patients with N2 involvement? Were those nodes actually located in the inferior mediastinum, which could have been overshadowed by the SUV activity from the mesothelioma at the pleuropericardial junction, or were they even higher (up around the paratracheal and so forth)? Several times in operations, we found that patients already had N2 disease in a lower location (we also investigated the possibility of EUS, but then you run into the difficulty of having a false-positive result because of the pleural disease, and so forth).
Dr Flores. All of these patients had level 7 nodes.
Dr W. R. Smythe (Houston, Tex). I enjoyed your article very much. I have 2 comments about the use of PET in these patients and 2 questions for you as well.
One of the problems with PET (and one of the idiosyncratic things about mesothelioma) is that when performing mediastinoscopy, one can find patients who have minimally or no enlarged lymph nodes, but every node station is positive. In addition, as you know, another problem with PET is that tumors of 5 mm or less are below the resolution of most machines.
Second, in ipsilateral nodal disease, there is the problem of the pleura abutting the nodes, and when one evaluates these scans, it is very difficult (because of the lack of anatomic definition) to determine with any degree of accuracy what is pleura and what is node, especially when the mediastinal tumor is thick. CT-PET may eventually be helpful here.
I have 2 questions. Medicare (and many third-party payers) does not routinely pay for PET scanning for mesothelioma as a staging test. I would be interested to know who paid for these 63 PET scans in your retrospective evaluation.
In addition, one of the major problems that we have after resection of these patients is radiographically determining early disease when it recurs. PET actually may play an important role here. You mentioned that you performed PET scans on a few patients in the postoperative period; do you plan to use this as a routine follow-up modality?
Dr Flores. As far as the first question is concerned, I do not know who pays for the PET scans.
Second, I believe that follow-up is useful in these patients if you would consider resecting the areas that have positive results or administering chemotherapy that would actually work in this disease. If we find lesions (eg, supraclavicular lymph node) in patients, we administer gemcitabine and cisplatin. I believe that finding recurrent mesothelioma in these patients is dependent on the type of treatment that you give them afterward.
Dr E. Vallieres (Seattle, Wash). Did any of your patients receive a chemical pleurodesis of some sort, talc or other agent, before their PET scan, and, if so, how long before? As we know, that could potentially create a significant inflammatory reaction and may result in higher SUV measurements that the tumor itself would not give. Along the same line, did any of your patients receive induction chemotherapy between the time of their PET scan and the actual exploration and thoracotomy? This could also have had some influence on the findings at surgery.
I appreciated your presentation and all the comments from the previous discussants.
Dr Flores. Eighteen of these patients did have talc pleurodesis. The shortest time period was 1 month before PET scan. This is a confounding variable that we cannot control for with this study. You are right, talc does cause an increase in the uptake on PET scan, but we do not have that data.
Ten patients in this study received induction chemotherapy; however, correlation with PET scan preinduction and postinduction therapy was not performed.
Related Article
J. Thorac. Cardiovasc. Surg. 2003 126: 11-15.
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