, researchers tracked 392 patients at UCSF with diffuse low-grade glioma for up to 20 years. The results were validated in two external cohorts of 365 patients.
This type of brain tumor strikes 20,000 people a year in the United States, most commonly in young adulthood or midlife. This happens due to its diffuse, undetectable nature.
Tumor cells grow slowly after resection, leading to recurrence and eventually culminating in malignant transformation and death, often in less than two years.
Diffuse low-grade glioma has two subtypes: astrocytoma IDH-mutant and oligodendroglioma IDH-mutant 1p19q-deleted, which were reclassified to match their microscopic appearance and molecular characteristics.
Studies that did not follow patients for as long as we did have raised questions about the need for maximal surgery, especially in oligodendroglioma.
Aggressive Surgery Increases Survival with Low-Grade Brain Tumors
Researchers found that those with larger post-operative and/or pre-operative astrocytoma lived a median of nine years post-diagnosis, compared to more than 20 years with smaller residual tumors.
Patients with larger post-operative and/or pre-operative oligodendroglioma lived a median of 19.9 years, compared to more than 20 years with smaller pre- and post-operative tumors.
Additionally, patients who had undergone a potentially riskier procedure, gross total resection (GTR), in which all of the tumor visible on an MRI is removed, lived longer than those with residual tumors.
Astrocytoma patients with residual tumors lived a median of 11.4 years, versus 16.2 years with GTR. Oligodendroglioma patients with remaining tumors lived a median of 22.2 years, compared to longer for GTR.
A surgical procedure called GTR-plus, in which a margin of apparently healthy tissue is resected together with the tumor led to extended survival for astrocytoma patients but did not demonstrate a significant difference for oligodendroglioma patients.
In addition to data from UCSF, the researchers drew from cohorts at Brigham and Women’s Hospital in Boston and St. Olavs University Hospital in Norway, totaling 757 patients, to understand the interactive effects of molecular, clinical, and treatment variables on tumor progression.
They looked at two pivotal periods in the disease’s trajectory: progression-free survival, which precedes recurrence, and malignant transformation-free survival, which marks the escalation of the tumor from a more manageable grade 2 to grades 3 and 4.
Drawing from data from the three patient cohorts, the researchers predicted that at least 75% of a tumor needs to be resected to improve long-term outcomes.
These findings put an end to the controversy that maximal resection may not be required for some low-grade gliomas. Even for oligodendrogliomas, there is no question that maximal resection is critical for enhancing survival.
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