Tumor Response Metrics in Neuro-Oncology: A Review

Despite the efforts spent in clinical trials in neuro-oncology during the last few decades, many challenges remain in the radiologic evaluation of brain tumors and metastases. This article aims to explain the current use of tumor metrics, especially in phase II clinical trials, to evaluate response to systemic therapy in neuro-oncology. We will discuss the imaging findings associated with progression and with partial, minor, or complete response to treatment, as well as the method of measurement, the distinction between disease-related and treatment-related changes, and inclusion of clinical symptoms to define treatment response and progression. The evaluation of response in brain tumors requires metrics that account for differences in response between high-and low-grade gliomas and specific tumor behaviors associated with radiation and immunotherapy, among other pitfalls. Advanced brain imaging techniques, such as perfusion and permeability imaging, should be incorporated into clinical trials to measure response to novel therapeutic agents more accurately. Learning Objectives: To understand the role of tumor metrics analysis and the main challenges and pitfalls of applying neuro-oncology imaging criteria.