Which of the following is seen on electron microscopy of medullary thyroid carcinoma specimens?: (A) Presence of electron-dense granules in the nucleus, (B) Presence of electron-dense granules in the mitochondria, (C) Presence of electron-dense granules in the endoplasmic reticulum, (D) Presence of electron-dense granules in the cytoplasm
Answer is D. Medullary carcinoma on electron microscopy reveals variable numbers of membrane-bound electron-dense granules within cytoplasm of neoplastic cells.