After the tumor surgery removal, it is necessary to establish whether all the tumor cells have been completely removed. To do this, the pathologist observes the edges of the portion of tissue removed during surgery under a microscope. This observation defines the surgical margin:
In cases where there are no tumor cells near the edges of the tissue removed, the borders are classified as negative;
In cases where there are tumor cells in the vicinity of the borders of the tissue removed, the borders are classified as exiguous;
In cases where there are tumor cells at the edge of the removed tissue, the borders can be classified as coincident, focally compromised, or positive, depending on the extent of tumor presence at the edges.