Can positron emission tomography (PET) be used to detect subclinical response to cancer therapy? The EC PET Oncology Concerted Action and the EORTC PET Study Group.

At the EORTC NCI New Drug Development Meeting in Amsterdam in 1994, a workshop, suggested by the EC PET (positron emission tomography) Oncology concerted action, was held to bring together many of those European PET centres investigating the use of [18F]FDG ([18F]2-fluoro-2 deoxyglucose) PET scanning as a measure of response to cancer therapy. Of the current 31 PET centres in Europe invited to contribute, 15 centres already had data and others expressed interest. Many of the groups were collaborating with local oncologists to measure tumour response to chemotherapy (12 groups) and radiotherapy (three groups) with this technique. Despite variations of methodology, and difficulties in data interpretation, assessment of tumour [18F]FDG uptake was thought to be a reasonable method for the functional imaging of tumours, assessing metabolic rate and providing a measure of tumour response. Broadly, pooling experience, it would appear that changes in [18F]FDG tumour uptake following one or two cycles of chemotherapy treatment was related to ultimate clinical responses. Patients showing most reduction in [18F]FDG uptake achieved the best clinical responses. Data were also available on the effect of chemotherapy on normal tissues and some data on the effect of radiotherapy and tumour response. It was concluded that changes in [18F]FDG uptake as measured with PET may provide useful information on clinical as well as subclinical response of tumours to anticancer therapy. This could be useful as a guide to early response to therapy as well as providing functional assessment of residual masses of disease. More specific markers of cellular proliferation e.g. [11C]thymidine, or [11C]- amino acids may provide even more accurate information. A strategy was outlined whereby PET scanning protocols could parallel EORTC early clinical trials so that [18F]FDG response information could supplement phase I and II clinical studies. Following these developments, an EORTC study group was formed under the auspices of the EORTC research branch, and the strategy for future development in Europe outlined.