For further investigation of the vertical and horizontal distribution of biomarkers in a tumor block, an EGFR positive human oral cancer tumor was cut into three pieces with an interval of approximately 20 µm. These samples in the same tumor block were named tissue #1, tissue#2, and tissue#3. Figure is the overlay of SECM images of tissue #1, tissue#2, and tissue#3. It reveals the 3D distribution of EGFR in tumor block.