[18F]FDG PET/CT criteria for treatment response assessment: EORTC and beyond

In the era of precision medicine, the optimization of oncological patient management with early and accurate tumor response assessment is crucial. In this scenario, [18F]fluorodeoxyglucose ([18F]FDG) positron emission tomography/computed tomography (PET/CT) has gained an important role in providing prognostically relevant information. The first PET-based scoring system proposed in 1999 was the well-known European Organization for Research and Treatment of Cancer (EORTC) criteria. From that moment on and over the last 20 years, several PET/CT criteria have emerged and have been adapted to enhance the response assessment for specific tumor types and/or therapies, with only a few of them endorsed by guidelines. In this literature systematic review, we aimed to list and discuss the most relevant PET/CT criteria proposed for solid and non-solid [18F]FDG-avid tumors. A literature search extended until November 2022 on the PubMed/MEDLINE database was conducted. The criteria used to assess the response were first classified according to treatment type and specific cancer type. Then, the main findings of the criteria were analyzed and discussed. A widespread effort to standardize and identify the best [18F]FDG PET response criteria tailored for each oncological treatment emerged, also considering the introduction of new biological therapeutic agents and the increasingly essential post-treatment application of [18F]FDG PET/CT in different cancer diseases. To improve their impact on daily clinical practice, however, most of the proposed criteria need to be further validated.