Evaluating the response to treatment by PET/CT in particular, but in general by molecular imaging modalities, is one of the most challenging issue in oncology, especially if can be done earlier than morphologic imaging modalities. In GIST patients, the use of PET and PET/CT with FDG was able to define metabolic responders as early as seven days after starting the treatment, by significant decrease or disappearance of radiolabeled glucose uptake in the tumor site/s. Such results prompted a reevaluation of RECIST criteria in these patients, which favored the introduction Choi's criteria (analysis of largest diameters and density of the lesion/s before and after the start of treatment with imatinib. Furthermore, the use of PET/CT changes within the lesion/s has been applied in several different, solid, tumors treated with target therapy agents (i.e. everolimus, erlotinib, etc.) by having a significant impact in the management of these patients. The open question is the timing of PET/CT and the true ability of such test in identifying non responder patients in order to avoid useless therapies to the patients and do not significantly increase the costs for the national healthy systems. In this setting, probably, specific multicentre trials, well designed by oncologists and nuclear medicine physicians, should be performed and evaluated.

Dear Ludwig

We have a few FDG PET/CTs in patients with GIST - I'll find the data and mail you

Kind regards

Susanne

@Susanne, thank you for the information. When I completed medical school I worked in internal medicine, particular in oncology, for about three years. At that time little could be done for tumor patients. So, it is impressive to see what can be done now e.g. in GIST.....hope that comparable results will be achieved in other solid tumors in future.....

@Seondo, we haven't examined patients one week after treatment, but it would be interesting to set up a study to assess the impact of PET for early follow-up. Usually the GIST patients are referred to us after two or three months. In colorectal tumors receiving FOLFIRI and anti-angiogenetic treatment we assess the therapeutic effect after two cycles of treatment. Overall, assessing early response with PET is a very promising topic and actually little is known about that.

Regarding the timing....according to our experience it is very dependent on the histology of the tumor and the treatment protocol. For example, in melanoma patients receiving Ipilimumab we perform the first follow up five weeks after onset of treatment, because the immunological treatment demands more time than conventional chemotherapy.

I will be abroad for the nexr two weeks - will find our data later and continue conversation on Res Gate

Dear Colleagues, thank you to opening such a discussion that faces on the difficulty of both nuclear physician and oncologist to perform the PET scan at the most appropriate time.

The introduction of new drugs and new skemes can generate confusion in the appropriate timing.

On the other hand, it is undoubful that we have a powerful diagnostic tool that can address the oncologist oto the best treatment planning, with an optimization of the costs as well (e.g.: stopping expensive therapies in case of early unefficacy of the drug).

So many colleagues could have an advantage if we could try to prepare a paper on this topic... What do you think about?

@Lorenzo, timing is really a big problem.... there are so many new approaches for treatment, which needs to be considered to apply the appropriate time interval for PET follow up studies. A paper to update the info about PET follow up in oncological patients would be fine.

Fine. Within the end of the year we could arrange some rows, maybe involving a resident...

Sounds good. Somebody has to coordinate the provided data..

You are the boss! :-)

I can try to ask a resident with the aim to produce the paper...

:-) mmm.....have to think about that..... but maybe someone else like to take over the role to write a review paper about this topic?