[Response evaluation in nuclear medicine : Criteria, results and pitfalls]

Established criteria to categorize metabolic tumor response to cytotoxic chemotherapies may not be suited to capture the effects of therapy with immune checkpoint inhibitors (ICI) or with kinase inhibitors (KI), such as BRAF or MEK inhibitors.

To assess the metabolic response to cytotoxic chemotherapy by positron emission tomography (PET) with ¹⁸F-fluorodeoxyglucose (FDG), the criteria of the European Organization for Research and Treatment of Cancer (EORTC) and the positron emission tomography response criteria in solid tumors (PERCIST) were conceived. The salient features of both criteria are detailed in a comparative way.

To date only retrospective data exist for the evaluation of therapies with either ICI or KI. They show that response to ICI cannot be reliably determined using the established criteria. Employing the EORTC criteria the responses to KI can be adequately ascertained so that the metabolic tumor response in FDG-PET is regarded as a surrogate marker for the efficacy of these drugs.

Tumor response to therapy with ICI cannot at present be assessed with FDG-PET. Responses to BRAF and MEK inhibitors are, however, assessable using the criteria that were originally developed to evaluate responses to cytotoxic chemotherapy.