Some tumors are difficult to remove completely because the margins of the tumor look similar to normal brain tissue.
This is especially true for infiltrative gliomas, which invade neighboring tissue as individual cells or small groups of tumor cells that can spread out over a wide area. In these cases, use of 5-ALA can help neurosurgeons find tumor cells that lie outside the margins of the tumor.
5-ALA is a compound (swallowed by the patient before the surgery, in a liquid solution) that causes malignant glioma cells to fluoresce. Using a modified neurosurgical microscope, the neurosurgeon can more easily identify and remove the main tumor mass, in addition to small clusters of tumor cells outside of the tumor margins.