Understanding the Diagnostic Timeline in DMG

Funding support provided by Chimerix/Jazz Pharmaceuticals. Content independently developed and published by OncLive.

The timeline from initial imaging to biopsy, molecular testing, and final diagnosis of diffuse midline glioma is shaped by both clinical urgency and logistical considerations. With in-house next-generation sequencing platforms, results can often be obtained in 10 to 15 business days, typically within two to three weeks of tissue collection. This relatively short turnaround is critical because the treatment planning process depends on having a precise molecular diagnosis rather than solely histologic findings. While radiology provides the first clues, accurate tissue sampling and processing remain the foundation for definitive classification of these tumors.

Obtaining diagnostic tissue is a delicate process, especially since biopsies in deep or eloquent brain regions carry risks, including hemorrhage rates of 1–2% per procedure. Surgeons emphasize the importance of not leaving the operating room without securing abnormal tissue that can be confirmed under the microscope, even if a definitive tumor diagnosis cannot yet be made during frozen section review. This precaution avoids the need for repeat biopsies, which increase risk and patient burden. Careful surgical planning, clear communication with pathologists, and awareness of the unique dangers associated with brainstem or internal capsule lesions are essential. Ensuring diagnostic adequacy at the first attempt is viewed as a critical step in the multidisciplinary workflow.

Close collaboration between neurosurgeons and pathologists plays a central role in achieving reliable diagnoses. Surgeons often work directly with pathologists during the procedure to confirm the tissue’s diagnostic value and, when possible, provide additional samples for sequencing. The ultimate goal is to preserve material for molecular analysis, as this data directly informs treatment decisions and eligibility for targeted therapies. Without sequencing results, oncologists cannot design effective therapeutic regimens, underscoring why coordinated intraoperative strategy and timely pathology review are indispensable in the management of diffuse midline gliomas.