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J Thorac Cardiovasc Surg 2003;125:938-944
© 2003 The American Association for Thoracic Surgery
General Thoracic Surgery |
From the Department of Cardio-Thoracic Surgery,a the Department of Radiology, Division of Nuclear Medicine,b and the Department of Biostatistics,c University of Alabama at Birmingham, Ala.
Read at the Twenty-eighth Annual Meeting of The Western Thoracic Surgical Association, Big Sky, Mont, June 19-22, 2002.
Received for publication July 10, 2002. Revisions requested Aug 19, 2002; revisions received Oct 7, 2002. Accepted for publication Oct 18, 2002. Address for reprints: Robert J. Cerfolio, MD, Associate Professor of Surgery, Division of Cardiothoracic Surgery, University of Alabama at Birmingham, 1900 University Blvd, THT 712, Birmingham, AL 35294 (E-mail: Robert.cerfolio{at}ccc.uab.edu).
| Abstract |
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| Introduction |
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| Methods |
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All FDG-PET scans were performed on a dedicated ECAT EXACT PET scanner (CTI). The scans were performed after injection of 370 MBq of FDG intravenously, and the chest CT was available at the time for correlation. The patients were advised not to eat or drink fluids containing calories for 4 hours before arrival at the PET center. This was confirmed with the patient before injection of the radiotracer. Any suspicious lymph node, nodule, or mass on the CT scan or that was visualized by means of FDG-PET was further evaluated by means of conventional radiography or biopsy. Patients were then clinically staged, and they received neoadjuvant therapy with chemotherapy (with or without radiation). All patients then underwent repeat staging with a second CT scan of the chest and a repeat FDG-PET scan. Any suspicious lesion or lymph node determined by means of FDG-PET or CT scanning underwent biopsy. Patients whose test results were initially negative for N2 disease (including those whose results were initially positive and then rendered negative by neoadjuvant therapy) underwent thoracotomy. Complete thoracic lymphadenectomy was performed, and frozen-section analysis were made. If the N2 nodes were negative in frozen-section analysis, pulmonary resection was performed. If the N2 lymph nodes were still malignant, pulmonary resection was not performed because no survival benefit has been shown, and the increased morbidity of pulmonary resection was avoided. Patients were excluded from this series if they did not have an initial FDG-PET scan before their neoadjuvant therapy or if the FDG-PET scan was not performed on a dedicated camera. All patients were staged by using the TNM classification system, as described by Mountain.
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Suspicious lymph nodes on FGD-PET scans were defined as any node with a mean standard uptake value (SUV) of greater than 3.0. This value was chosen on the basis of work previously performed and based on our center's mean mediastinal background SUV of 1.63 (SD = 0.31). Suspicious lymph nodes on CT scanning were defined as any N2 lymph node that was larger than 1.0 cm in any axis. This value was chosen to ensure that any lymph node that was even slightly enlarged on CT, whether in the short or long axis, underwent biopsy. Any indeterminate lesion outside the thorax underwent further investigation, biopsy, or both. The same criterion was used after the completion of the neoadjuvant protocol. However, if the initial FDG-PET scan questioned a lesion, a biopsy of the lesion showed it to be negative, and repeat FDG-PET showed the lesion to have the same SUV or less, repeat biopsy was not performed. However, if the lesion had a higher SUV or if the patient had a new suspicious lesion, it underwent biopsy.
Patients who underwent chemotherapy for biopsy-proven N2 disease underwent rebiopsy of the same N2 node after chemotherapy. If that node was still positive, the patient did not undergo thoracotomy but was included in this trial. Patients who were entered into the American College of Surgeons Oncology Group S9900 trial and who were randomized to chemotherapy were also included in this study. All patients who underwent thoracotomy and who had resection of their pulmonary lesion with intent to cure underwent complete thoracic lymphadenectomy. Pulmonary resection was performed by means of pneumonectomy, lobectomy, or segmentectomy only.
All results are reported as ranges with medians. Comparisons were made by using a Kruskal-Wallis
2 test and comparison of population proportion with a Fisher exact test if needed. Table 1 depicts the definitions and calculations used to determine the sensitivity, specificity, accuracy, negative predictive value, and positive predictive value. The internal review board at the University of Alabama at Birmingham approved this study.
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| Results |
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Nine of the 34 patients did not undergo resection. Five patients with N2 disease had recalcitrant N2 disease. In 3 patients the disease was determined preoperatively through endoscopic ultrasonography with FNA, and in the other 2 patients the disease was proven at the time of thoracotomy. Three patients had progression or lack of regression of disease, had T4 disease at the time of exploratory thoracotomy, and did not undergo definitive resection. The final patient was found to have a metastatic nodule in another lobe of the same histologic type at the time of thoracotomy and did not undergo resection (Table 3). The remaining 25 patients underwent pulmonary resection and complete thoracic lymphadenectomy. The types of resections were lobectomy in 19 patients, pneumonectomy in 4 patients, and segmentectomy in 2 patients. All patients who had pulmonary resection also underwent complete thoracic lymphadenectomy. The final pathology after chemotherapy, surgical resection (or both) or restaging is shown in Table 3
. One patient underwent lobectomy, and although the N2 lymph nodes were all determined to be negative in frozen samples, he was found to have a microscopic deposit of cancer in one N2 lymph node on final pathologic examination.
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| Discussion |
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Akhurst and colleagues
16 found that FDG-PET scanning after induction therapy accurately detected viable primary tumor but not the involvement of mediastinal lymph nodes. Unlike that study, we compiled data for each lymph node station and also subdivided the N2 lymph nodes into the mediastinoscopy-accessible paratracheal nodes versus the rest of the N2 nodes. Also, in the report by Akhurst and colleagues, there were 56 patients, although only 14 had an initial FDG-PET scan before neoadjuvant chemotherapy that was available for comparison. In our series, similar to the study of Akhurst and colleagues, most patients had chemotherapy only, but unlike their series, all of our patients had an initial FDG-PET scan before the chemotherapy for comparison.
Careful analysis of Tables 6
and 7
shows that FDG-PET scanning is at least as good and usually superior to CT scanning in all categories. It is more specific, has a higher positive predictive value, and has a higher negative predictive value than CT scanning for detecting residual tumor in the primary mass. Only FDG-PET scanning correctly predicted complete resolution of disease in the 4 patients who had T0 N0 disease (complete responders). When the FDG-PET scan was incorrect for the T status, it was because it could not accurately differentiate a T3 lesion from a T2 lesion or it failed to detect a T4 lesion (a small satellite nodule in the same lobe). FDG-PET scanning could not differentiate a small satellite T4 lesion in the lung (ie,
5 mm) from a metastatic N1 lymph node. FDG-PET scanning could not differentiate a T3 tumor with chest wall extension from a T2 lesion unless the CT scan was viewed concomitantly, as it was in this series.
FDG-PET scanning did not offer any significant advantage over CT scanning in the diagnosis of N1 lymph node metastasis. This is especially true in this series because patients with T1 small tumors were not included. Most patients had large bulky T2 or T3 lesions, and these large tumors obscure the intrapulmonary regional lymph nodes. It is therefore imperative that FDG-PET scans be reviewed, along with the current CT scan. In some cases fusion of functional FDG-PET and anatomic CT images with software programs might offer some advantage over visual correlation. PET-CT systems, which feature a PET and CT scanner in one machine, are acquired in one sitting for the patient. They are registered and fused to form a single 3-dimensional image that shows the anatomic location from the CT scan, along with the metabolic activity of PET. This type of system might provide the best way to image N1 nodes in the future. Randomized trials of CT-PET scans are needed.
As described above, perhaps the most important finding in this series is in patients with N2 disease. Although only 11 patients in this report had N2 disease, repeat FDG-PET scans correctly predicted the absence or presence of cancer in all the N2 paratracheal lymph nodes in all patients. However, as we found in our previous report,
18 FDG-PET scanning is not as accurate in the other N2 stations. It seems less accurate in the number 5, 6, and 7 lymph node areas. This is valuable information for the surgeon.
The real question is whether 2 FDG-PET scans are cost-effective and whether it adds enough information not given by the repeat CT scan that makes this additional cost worth it. This article seems to suggest that it is worth it, although a cost analysis was not performed.
All patients received chemotherapy, and 27 of the 34 patients received chemotherapy only. Because FDG-PET scanning seems to be sensitive without false-positive results at any time during chemotherapy, perhaps its true importance might be to help us tell who is responding to chemotherapy after 1 or 2 cycles. Perhaps, in the future, if a patient is not responding to the preoperative regimen (as determined by means of repeat FDG-PET scans), then a different chemotherapeutic regimen, radiation, or both could be added early in the neoadjuvant therapy. Although we only had 7 patients who received radiation in this trial and the numbers were too small to make any solid conclusions, radiation, in our experience, can lead to a false-positive FDG-PET result for up to 6 months.
In conclusion, repeat FDG-PET scanning is a highly accurate noninvasive test that helps predict the T and N2 status in patients with NSCLC who have undergone neoadjuvant chemotherapy. It is superior to CT scanning in predicting the absence or presence of residual cancer in the primary tumor and in N2 nodes, especially paratracheal lymph nodes. Its role in this setting, especially in patients with N2 disease, requires further prospective multi-institutional trials.
| Appendix: Discussion |
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Your own expectations of PET providing this information are more optimistic than my own. Your series is certainly intriguing and provides a preliminary indication of efficacy. However, the knowledge of how PET works makes me skeptical that this will provide a major clinical benefit. The sensitivity of PET is dependent on tumor cell volume, tumor density, and cellular avidity for fluorodeoxyglucose. Microscopic disease could easily be missed with our current technology, resulting in poor sensitivity. On the other hand, the effects of treatment, particularly radiation, might produce fluorodeoxyglucose uptake in the absence of tumor, resulting in poor specificity and the tragedy of clinical overstaging.
I note that the majority of your patients had chemotherapy alone without radiation, and this is partially due to enrollment in the S9900 clinical trial. However, most centers treat patients with N2 disease with combination chemoradiotherapy. Do you think that inclusion of radiation will likely confound the positive predictive value of PET that you found in this series?
The only other question I have concerns the rationale of separating out paratracheal lymph nodes from other mediastinal lymph nodes in your analysis. I know of no evidence from centers other than yours of a difference in PET accuracy for different N2 nodal stations. I also do not know of evidence that one group of nodal stations confers a difference in prognosis or treatment recommendations. Is there a good reason for complicating this analysis by separating out 2 different sites of N2 nodal disease, and does this have clinical significance?
Dr Cerfolio. Thank you very much, Dr Wood, for the kind comments. I appreciate them.
As you mentioned, as a pioneer in some of this PET scan work, I would like to have some confirmation from other centers to show that we are either right or way off base, but it would be nice to get some confirmation. That leads me to your second question first. We have shown, in the article that we presented at the meeting of The Society of Thoracic Surgeons this past year on PET scanning, that PET scanning does seem to have a different accuracy, sensitivity, and specificity in different N2 lymph node stations. Whether that is important, I do not know, but we do know clinically that patients with left upper lobe disease that have number 5 and number 6 N2 involvement have higher survival of especially adenocarcinomas than those who have N2 disease in a right upper lobe with number 2 and number 4 involvement. Therefore there might be clinically important prognostic indicators from that. We have found that in the number 7, number 5, and number 6 lymph node stations, PET scanning is a little less accurate than it is in the number 2 and number 4 stations. I think that answers your second question first.
Your first question is about the radiation. There is no question that we have seen that radiation leads to false-positive PET results up to 6 months and even up to 6.2 months in one patient, so at least 6 months. For that reason, we prefer chemotherapy. We also think oncologically that chemotherapy is better for patients with N2 disease because it better tests the biology of a patient's tumor. If they do not respond to chemotherapy, because most patients with N2 disease fail systemically, we do not think they should be treated with resection. Radiation does not test that biology as well as chemotherapy, and therefore we prefer just chemotherapy for N2 disease, as opposed to chemotherapy and radiation.
Dr Wood. I just want to follow-up on your first answer because I think that we are talking about 2 different things. With regard to the aspect of separating lymph node stations out, I agree that for very specific circumstances, there might be different prognostic implications of, for example, a station 5 lymph node for a left upper lobe tumor, but that is not what your article is about. Your article is about detecting response to therapy, and in your algorithm you have decided to not treat patients surgically that have persistent N2 disease or any N2 disease. Therefore essentially, it is an all or none phenomenon, and it does not matter whether it is a 4R lymph node, a 5, a 7, an 8, or a 9. I would ask you again, why is it necessary to separate those out?
Dr Cerfolio. The reason we separate out the different lymph node stations is because we believe the strength of PET is that it helps inform the surgeon where and how to target biopsies for N2 disease. If it is more accurate in one N2 station compared with another, then one may choose a mediastinoscopy or an esophageal ultrasound with FNA over video-assisted thoracic surgery or a Chamberlain procedure, etc. Also, in the future, we may find a difference in survival or prognosis; as good scientists, our job is to present the data. For instance, we may later find that there is a difference in survival or recurrence patterns for different stations: for instance, we now know that a positive No. 9 station is a bad actor. For these reasons we think it is important to report the difference accuracy for the N2. Another reason is that, unfortunately, not all the patients are seeing surgeons, and a lot of oncologists are using PET scans to deny people operations. What we are trying to tell them is to be careful, that all patients need biopy for all stations, but that in certain stations the PET scan is even less accurate than it is in others. The bottom line is biopsies are still needed.
Dr John Benfield (Los Angeles, Calif). If I understood correctly, you did not proceed with resection when, after induction therapy, the mediastinal lymph nodes remained positive. That certainly is a reasonable approach with which I agree. I was not clear what you do when the intralobar lymph nodes, the N1 lymph nodes, are positive after induction therapy.
Dr Cerfolio. We perform resection in those patients.
Dr Benfield. Why do you do that?
Dr Cerfolio. Our belief is that it not only improves local control but potentially improves survival. The jury might be out on that, but our belief is that it is probably going to lead to improved survival.
Dr Benfield. I will look forward to additional data on that point because it is my belief, my hypothesis at least, that after induction therapy, an N1 lymph node that remains positive is evidence of systemic disease. I would predict that long-term results will show that such patients also do not benefit from resection.
Dr Cerfolio. What if the patient started off with an N2 lymph node? You just asked what do we do with N1, and therefore if they have been downstaged from N2 to N1, we would resect. If they have N1 disease and continue to have N1 disease, that is a different situation. We treat them by resection, but I think that their survival benefit might be less. I concur.
Dr Benfield. I am just giving you food for thought and a basis for next year's article.
Dr Cerfolio. Thank you.
Dr Thomas Rice (Cleveland, Ohio). I want to ask about microscopic residual disease. How often did you find it, and how often was PET not able to see it? You have very good sensitivities and positive predictive values, which means the tumor is still there. Do you think this is more effective in ineffective chemotherapy than good PET scanning, and how do you use the information when your PET scan says that the patient has persistent N2 disease after induction chemotherapy? Would you perform a biopsy of those nodes or not perform an operation on that patient?
Dr Cerfolio. I will take the last question first. We do a biopsy of every node, no matter what the PET scan shows, to determine whether it is correct or incorrect. If the patient has residual N2 disease, we resect only if the patient is young with low risks and if we can resect without doing a pneumonectomy.
As to the question about microscopic disease, it depends on how you define it. If the pathologist very carefully cuts the specimen, one might find microscopic disease and one might not. The ones where results indicated the patients were complete responders, we asked them to go back and very carefully cut, and they found no microscopic disease. Certainly PET scanning is going to miss microscopic disease of less than 6 mm, and we found that in this series as well.
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