Normal adrenal medulla on the left (with its typical “nests” of cells) and its malignant counterpart, pheochromocytoma, on the right. These are taken at the same magnification, so you can appreciate how large and atypical the cells are in the pheochromocytoma. Even if this lesion were not destroying the normal adrenal medulla and cortex (it was) or invading the capsule of the adrenal gland, you would know that it is malignant based on the cytologic atypia and mitotic activity (no mitoses are seen in this photo). Most of the cells present in the photo are in the malignant clone, showing the variability within the same cancer. These tumors often cause autonomic nervous system dysfunction, particularly hypertension, due to their secretions.