Therapy monitoring with PET in cancer patients: achievements, opportunities and challenges ahead for the PET community

Abstract

It has been 18 years since the first guidelines on PET response criteria were released [1] (with little supporting data at that time) and 15 years since the first successful use of PET for evaluation of a molecularly targeted therapy (imatinib) was published [2]. This latter study demonstrated the huge potential of PET imaging in assessing tumor response early after treatment initiation, at a time when conventional criteria based on size measurements (RECIST) were found to be unsatisfactorily. Since then, numerous studies using FDG PET as a surrogate marker to evaluate response to therapy have been published; PET Response Criteria In Solid Tumors (PERCIST) have been introduced [3,4] and data regarding repeatability of PET have been published, supporting the use of thresholds to discriminate between responders and non-responders [5,6]. Nonetheless, unfortunately, FDG PET is far from being a standard tool in clinical trials assessing new antineoplastic tools, but there have been indeed relevant progress.It is our pleasure to introduce this special issue of the EJNMMI dedicated to therapy monitoring with PET in cancer patients, in which the reader will find up-to-date information on the basis of tumor biology and new PET technologies for therapy assessment with FDG and other PET probes in solid tumors and in hematological tumors.We have divided the issue into four sections. The first section includes a recent update on PET technologies and two articles discussing the motivations and methodology for harmonization of PET data and the challenges faced when implementing PET in clinical trials. It is followed by a section including a practical guide to better understand molecularly targeted therapies, and a comprehensive review on the use of the EORTC PET response criteria as well as the PERCIST. The third section reviews therapy monitoring with 18 F-FDG, 18 F-or 11 C-Choline, 68 Ga-PSMA and Sodium Fluoride in solid tumors, while the fourth and last section reviews therapy monitoring in hematological malignancies.One might consider that the natural history of PET technologies and antineoplastic drugs is somewhat similar, both being characterized by continuous improvements and from time to time a major breakthrough. In this EJNMMI special issue, Van der Vos et al. [7] review hardware (digital PET) and software (advanced reconstruction algorithms) PET technological improvements, digital PET being expected as a major breakthrough by the PET community. While these advances give our community great opportunities such as a better staging capability thanks to an improvement in small lesions detectability, they also bring challenges in getting harmonized images/quantitative values in PET centers running different PET systems and in multicentre clinical trials, as reviewed by Aide et al. [8] in a paper also discussing the EANM response to this issue, namely the EARL accreditation program. Yet, harmonization of PET data is only one of the problems faced by the medical oncology and PET communities when trying to implement PET wi...