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Ann Thorac Surg 1997;64:769
© 1997 The Society of Thoracic Surgeons
DR WALTER J. SCOTT (Omaha, NE): Our group has had a lot of experience with lung cancer and positron emission tomographic (PET) scans. Do you perform transmission scans as well as emission scans when you do the abdominal studies?
DR LUKETICH: Are you talking about dynamic imaging?
DR SCOTT: No, I mean some type of an attenuation correction study.
DR LUKETICH: Yes, we do that.
DR SCOTT: So both the chest and abdomen had attenuation corrections?
DR LUKETICH: The dynamic images acquired over the chest were attenuation corrected, but the whole-body images were not.
DR SCOTT: Do you have any idea what the standardized uptake values of the lymph nodes were?
DR LUKETICH: The ones that were missed on PET scan but positive on biopsy?
DR SCOTT: Right.
DR LUKETICH: They tend to be close to 1, 1 to 1.5, or you do not see them at all. The problem with the standardized uptake value is that when there is not a subjective call, there is nothing to measure. There is nothing in your region of interest, so it is hard to calculate a value. You need a subjective area, a region of interest from which to calculate. We found that in almost every case when there was a substantial light-up on the PET scan, the standardized uptake value was in the range of 2 or higher. I think that it is a little more problematic in lung cancer, where you have hyperplastic nodes that give those false-positive readings. In our study, we did not see any false-positive findings in terms of the nodal evaluation. There were a couple of false-positive bone images by PET but no false-positive lymph nodes or liver readings.
DR SCOTT: Were the lymph nodes that were missed near the primary tumor?
DR LUKETICH: Yes, in all cases they were. They are the periesophageal nodes.
Would better resolution solve this problem? We are investigating some other tracers that may allow better resolution. We are also investigating dynamic scanning in those areas that may allow better resolution. But right now for nodes smaller than 1 cm, I think we missed a significant number in our series. When a histologically positive but small lymph node is present, in the 2- to 8-mm range, there is a good chance you will miss those nodes by PET, just as we missed a 2-mm liver metastasis.
DR SCOTT: Would that have changed the operative approach?
DR LUKETICH: The question is, How are we going to clinically utilize PET scanning in patients with esophageal cancer? If the PET scan is negative for distant metastasis, then I think it depends on your philosophy. At our institution, if a PET scan shows the primary only, the patient undergoes staging by video-assisted thoracoscopy or laparoscopy. If that staging is truly negative for nodal involvement, then we go on to surgical resection alone. But if the staging by video-assisted thoracoscopy or laparoscopy is positive for nodes, the patient is entered into a neoadjuvant TaHol (paclitaxel)–inclusive protocol.
Likewise, at the other end of the spectrum, if our PET scan identifies distant metastases, and that represents about 20% of patients, they receive nonsurgical treatment such as an expandable metal stent or photodynamic therapy.
DR KEITH S. NAUNHEIM (St. Louis, MO): My colleagues and I have been using the PET scanner as well, specifically before and after neoadjuvant therapy. I wonder if you have any experience with PET scanning after neoadjuvant therapy in regard to the sensitivity and the specificity of determining complete resolution of disease. Do you think this will be a good predictor of who is going to be a complete responder and who is not? This would help us determine which patients should receive further therapy.
DR LUKETICH: As you are probably aware, there are some PET data in the literature on head and neck cancers after treatment. We have about a dozen anecdotes about patients with a variety of malignancies for whom we used a PET scan as a last call on whether we were going to return the patient to the operating room after adjuvant therapy. For example, a patient was found to have extensive nodal involvement and unresectable disease on staging by video-assisted thoracoscopy and laparoscopy. The patient then received five cycles of chemotherapy, was rescanned, and showed a dramatic decrease in nodal involvement on follow-up PET scan. He did not have any distant metastases, underwent resection, and was confirmed to be downstaged.
The real question is, Who is going to pay for this treatment? Right now, the institution will not, nor will the insurance companies. We are having trouble in that setting because we need several PET scans to evaluate the ongoing response to treatment.
DR LEUKETICH: Thank you.
DR NAUNHEIM: I echo your findings with PET scanning for esophageal cancer. Approximately 17% of our patients have had distant metastases that were entirely unexpected. When I compare this to computed tomographic scanning or endoscopic ultrasound, this is probably one of the most exciting noninvasive staging tests we have developed. I think it can prevent a futile thoracotomy in a significant percentage of patients. I congratulate you on your work.
Related Article
Ann. Thorac. Surg. 1997 64: 765-769.
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