New Classification System Brings Clarity to Brain Tumor Surgery Decisions
Posted on 05 Feb 2026
Low-grade brain tumors known as IDH-mutant gliomas (CNS WHO grade 2) are life-threatening despite their slow growth. Surgeons must balance maximal tumor removal against the risk of neurological deficits, but the absence of standardized criteria hampers outcome comparability. To help address this challenge, an international team has introduced a classification that standardizes how residual brain tumor is assessed after surgery.
The Response Assessment in Neuro-Oncology (RANO) classification was developed by an international working group involving Friedrich-Alexander-Universität Erlangen-Nürnberg and Uniklinikum Erlangen. It defines operative success based on the volume of tumor remaining visible on a specialized postoperative MRI sequence, T2 fluid-attenuated inversion recovery (T2-FLAIR). The system establishes a common language for describing the extent of resection in IDH‑mutant WHO grade 2 gliomas.
Investigators conducted a large international study involving 1,391 patients treated at 16 specialized neuro-oncology centers. The analysis revealed that lower residual tumor volume after the initial surgery is a critical determinant of disease progression. The advantage of more extensive resection was also observed in oligodendrogliomas, which typically have a more favorable prognosis and respond well to chemotherapy and radiotherapy. Notably, adjuvant treatments such as chemotherapy or radiation did not offset the impact of the initial surgical outcome.
The findings were confirmed in an independent patient cohort at the University of California, San Francisco. The classification supports more consistent surgical decision-making and provides a framework for future studies. Results were published in The Lancet Oncology.
“The new RANO classification is a milestone that will make a significant impact on neuro-oncological research and care in the long term,” said Prof. Dr. Oliver Schnell, Uniklinikum Erlangen.
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