Infiltration / invasion

What it is

Infiltration (or invasion) is the spread of glioma cells into the surrounding normal brain tissue. This infiltrative behavior is the defining feature of diffuse gliomas and is the main reason they are difficult to remove completely.

Understanding Infiltration / invasion

Diffuse gliomas do not stay within a sharp boundary; their cells extend, often microscopically, into the adjacent normal brain — sometimes well beyond what is visible on imaging. This blurs the line between tumor and healthy tissue. As a result, even when a surgeon removes all the visible tumor, infiltrating cells typically remain in the surrounding brain, which is why diffuse gliomas tend to recur and why surgery is usually combined with radiation and chemotherapy that can address the infiltrating cells. Infiltration also explains why these tumors are considered malignant even when low-grade and slow-growing. Understanding infiltration clarifies the central challenge of diffuse gliomas — their spread into normal brain — and why treatment must address more than just the visible mass. It is fundamental to how these tumors are managed. Understanding infiltration clarifies the key behavior of diffuse gliomas.

Why it matters

Understanding infiltration helps patients and families see why diffuse gliomas are so challenging — their cells spread into normal brain beyond the visible tumor, making complete removal difficult and combined treatment necessary.