Golden rules for optimizing the diagnostic pathway of IDH-mutant tumors: bridging evidence and clinical practice in cholangiocarcinoma and adult-type diffuse gliomas

Background: Mutations in the isocitrate dehydrogenase (IDH) genes are key biomarkers in intrahepatic cholangiocarcinoma (CCA) and adult-type diffuse gliomas, although real-world adoption of comprehensive molecular diagnostics remains uneven. This review aimed to integrate published evidence, clinical experience, and international guidelines to provide pragmatic recommendations that can standardize IDH testing across healthcare systems. Methods: A multidisciplinary panel synthesized data identified through 10 PICO-driven questions, critically appraised guideline statements from ESMO, EANO, NCCN, and WHO-CNS5, and incorporated insights from clinical evidence on IDH molecular profiling in CCA patients. Recommendations were developed through interactive expert discussion. Results: The panel addressed six issues: (i) positioning of next-generation sequencing (NGS) as a first-line assay; (ii) using liquid biopsy to supplement inadequate or uninformative tissue-based molecular analyses; (iii) tumor-adapted workflows combining immunohistochemistry, PCR, or NGS with large genomic panels; (iv) optimizing pre-analytical management of small biopsies in terms of neoplastic cell abundance and nucleic acid fragmentation to safeguard material for integrated testing; (v) evaluating promising biomarkers based on genome-wide methylation profiling and metabolic imaging in specialized centers; and (vi) novel testing strategies including centralized and decentralized algorithms. In addition, emerging approaches based on digital pathology, teleconsultation, and harmonized reimbursement pathways were discussed. These considerations were distilled into a set of "Golden Rules." Conclusions: Optimized molecular profiling is a cornerstone of precision oncology in IDH-mutant tumors, but the lack of harmonized procedures hinders its widespread implementation in the clinical setting. In intrahepatic CCA, upfront NGS should be prioritized to capture the full spectrum of actionable alterations, whereas in diffuse gliomas IHC for IDH1 p.R132H remains recommended, with PCR or NGS reserved for IHC-negative or equivocal cases. Advanced tools such as genome-wide methylation profiling or metabolic imaging may add value in specialized centers. The consensus-based "Golden Rules" pragmatically support harmonization of diagnostic workflows, reducing technical costs and turnaround time, and promoting equitable access to IDH-directed therapies across diverse healthcare settings.