The silent phase of diffuse low-grade gliomas. Is it when we missed the action?

Background: It is commonly believed that, before being diagnosed after onset of symptoms, diffuse low-grade glioma evolve silently for a long time. The present study aimed to estimate for the first time the exact duration of this silent phase, during which the glioma is radiologically visible but undiscovered.

Methods: We retrospectively reviewed our French national database of diffuse low-grade glioma, searching for patients with an MRI-based assessment of their velocity of diameter growth at diagnosis and before any treatment (at least three MRIs over more than 6 months). For each patient, the duration of the silent phase was estimated by the formula: duration = initial diameter / initial velocity of growth.

Results: A total of 148 patients were included in the study. The mean lead-time duration (i.e., duration of the silent phase) was 14.0 ± 7.8 years (median, 11.6 ; range, 1.6-39.4). The lead-time is statistically not correlated to the tumor volume. It is markedly decreasing with the velocity of diameter expansion.

Conclusions: Diffuse low-grade glioma are radiologically detectable but clinically silent for more than a decade. Such a long period of silent evolution could explain our current failure to cure these tumors. It can also be viewed as a window of opportunity to detect these tumors earlier, suggesting the need to set up a screening program.