Conference Vancouver, B.C. June 11, 2001
Speakers
Dr Sutcliffe: Thanks, I would just like to just finish up now with Primary Unknown. We talked about cervical nodes and suspected Head and Neck cancer where we felt that that was a strong indication for PET. In Primary Unknown in general the recommendation is that PET scanning is an appropriate procedure. Any equivocation about that or any concerns or interpretations?
Dr Wahl: Well I hate to be negative, but if you want to take an evidence base there are only about two papers about it. I think clearly we need to grow the literature and if you do allow it to be done here I think it would be useful to see how often it does change what is done for the patient. Some do take a more nihilistic view on this in that if you can’t figure out where it is from then it may not make a whole lot of difference in most instances although. So I would say the evidence isn’t as strong there as I feel it is in some of the other conditions though I would certainly not be opposed to it being applied carefully.
Dr Sutcliffe: Other comments? Joe?
Dr Connors: Yes, I just want to pursue that a little bit because I think there is a big difference between identifying the primary and actually finding out something that is of clinical utility for the patient in cancer of Unknown Primary. It’s the aspect of managing these patients that has bedevilled caring for them for the whole time that they have been defined as a separate entity and it is not infrequent that one does actually define the primary with absolutely no utility to the patient whatsoever. So I would want to narrow that down, or extract more from the data, and find out how often the patients actually have treatable primaries discovered that is treatable in the sense of disease that you can meaningfully manage or modify the natural history of metastatic disease once you discover it. And I suspect that that one third of patients that are found to have primaries would shrink to one tenth perhaps (?) of times when you actually find out they have an illness that you can change the natural history in a meaningful fashion. In which case you would be doing 10 PET scans for each time you found one that was of any utility in the patient at all.
Dr Conti: This is an interesting paradox in a sense because you have a situation potentially where you can do a PET scan to find a primary and you are saying basically that might not be able to do much with that PET as far as patient management but interestingly that the same time that you are doing PET scans to look for the primary you are also potentially staging the disease so you may in fact find the primary, find the diagnosis and also determine whether or not, given that new cancer that you have identified is in fact treatable or not treatable. So for example lets say it was a thyroid cancer for the sake of argument and you were able to resect disease. Then it would be potentially a curable cancer from that patients perspective on the other hand it might be something like metastatic carcinoma from another source and be completely incurable, in both cases you have identified the tumour and one might be treatable and not be treatable and even between those different types of cancers it is the extent of disease to determine whether or not you could manage the patient effectively. So it is a bit of a paradox in a sense. You could get the information to help you on both ends.
Dr Connors: That is why I think it is necessary to characterize the question in terms of seeking additional information on those situations where you can conceive of it modifying further treatment.
Dr Sutcliffe: Dr Wahl? Dr Shreve? Dr Jones?
Dr Wahl: Let’s see. The kind of interesting issue though, it seems like the oncologists in the room all know the standard work up of the cancer of unknown primary. So probably unhesitatingly are going ahead and doing that CT and the whole body, mammogram, additional studies, may be not so but I would just say for those who aren’t that is the logic that would seem reasonable because if you are going through the full work up it would seem that PET would also be a rational part of the full work up of an unknown primary. So it seems like the decision might be to come up even earlier in your thought process when you are using conventional diagnostic methods. If you are going to go through all those it seems only reasonable to do PET because there is an incremental yield but if you don’t think that it is going to make any difference where this primary is from then you might question why do the CTs and everything else.
Floor: Just a plea to be a bit more rational in the selection of PET scanning in the assessment of patients during follow up for example I don’t take care of patients with GI malignancies but my suspicion is that if the CEA is rising rapidly 3 or 4 months after primary treatment, that that patient isn’t likely to have salvageable disease unifocal metastases that are amenable to high grade palliation. In contrast in someone whose CEA starts to rise 18 months or 2 years after the completion of primary treatment and not to discount the value of follow up but to try and employ the circumstances where there is some biological potential to really make a difference with the treatment.
Dr Jones: I think I’d just like to reiterate that I. There is so little literature available on the Primary Unknown with metastases to sites other than cervical nodes that I think that this is a research area really rather than a primary tool. I think it does have a role where you may be thinking of a surgical procedure on a patient with primary unknown, where you think that the primary say metastasis in the liver may actually be rather than a metastatic adenocarcinoma it may be a paracellular carcinoma and you may be looking at a surgical procedure, I think it has a role already but I think with respect to the utility of making a diagnosis of a primary that is something that should be really part for a research protocol.