TABLE 17-4.

Common Ultrastructural Features of Tumors

Tumor Type	Cellular Features	Extracellular Matrix
Adenocarcinoma	Microvilli. Lumens. Junctional complexes. Secretory granules. Golgi apparatus. Endoplasmic reticulum. Cilia (+/−).	Basal lamina
Carcinoid/islet cell tumors	Insular arrangement of cells. Intercellular junctions (e.g., desmosomes). Numerous dense-core granules (variable size and morphology depending of tumor type). Variable intermediate filaments.	Basal lamina surrounding cell clusters Collagen
C-cell carcinoma of thyroid	Dense-core granules. Variable number of organelles (Golgi apparatus, RER, mitochondria).	Basal lamina surrounding cell clusters Collagen
Chondrosarcoma	Scalloped or villous-like cell surface. Abundant and dilated RER. Large Golgi apparatus. Abundant glycogen. Variable intermediate filaments.	Variable. Collagen, glycoprotein, glycosaminoglycans
Fibrosarcoma	Abundant rough endoplasmic reticulum. Cytoplasmic filaments. Golgi apparatus. Filopodia (+/−).	No basal lamina. Abundant collagen.
Gastrointestinal stromal tumor	Lack of distinct nuclear/cytoplasmic features or morphology similar to smooth, fibroblastic or nerve cells.	Basal lamina (+/−). Collagen.
Glomus tumor	Epithelioid cells. Many mitochondria. Thin filaments. Dense bodies. Pinocytotic vesicles.	Basal lamina. Collagen.
Granular cell tumor	Tightly apposed cells. Numerous cytoplasmic, membrane-bound, variable electron-dense granules (secondary lysosomes).	Basal lamina around groups of cells.
Hemangiopericytoma	Palisading arrangement around capillaries. Focal attachments and intercellular junctions. Pinocytotic vesicles. Intermediate filaments. Variable number of mitochondria, RER.	Abundant basal lamina and matrix.
Hemangiosarcoma	Prominent junctional complexes. Villous-like projections on the luminal aspect. Pinocytotic vesicles. Intermediate cytoplasmic filaments. Free ribosomes. Some mitochondria and RER.	Basal lamina.
Histiocytic sarcoma	Variably sized and shaped nuclei. Numerous cytoplasmic organelles (lysosomes, mitochondria, Golgi apparatus, lipid droplets [+/−]). Phagocytosed red blood cells or leukocytes (+/−).	No basal lamina.
Langerhans histiocytosis	Large, irregularly shaped nucleus. Numerous organelles (mitochondria, free ribosomes, rough endoplasmic reticulum, primary lysosomes). Filopodia. Absence of secondary lysosomes.	No basal lamina.
Leiomyosarcoma	Thin (6-nm) filaments and dense bodies among filaments within cytoplasm and subjacent to plasmalemma. Pinocytotic vesicles. Little RER. Round-ended nuclei. Contraction indentations of nuclei.	Basal lamina.
Leydig cell tumor	Lipid droplets. Abundant SER. Mitochondria with tubular cristae. Microvilli on cell surface. Canalicular-like spaces between cells.	Partial basal lamina.
Liposarcoma	Lipid droplets. Pinocytotic vesicles. Glycogen (+/−). Intermediate filaments. Mitochondria (+/−), Golgi apparatus (+/−), SER and RER (+/−).	Basal lamina.
Lymphoma	Many free ribosomes or polyribosomes. No intercellular junctions. Smooth, indented or convoluted nuclear membrane	No basal lamina.
Mast cell tumor	Round, indented nucleus. Numerous membrane-bound cytoplasmic granules of variable density. Filopodia	No basal lamina. Collagen.
Meningioma	Long, interdigitating cellular processes. Numerous intermediate filaments. Numerous intercellular junctions (e.g. desmosomes). Variable number of organelles. Glycogen (+/−).	Basal lamina (−/+).
Mesothelioma	Numerous long microvilli. Intercellular junctions. Filaments. Tonofibrils. Glycogen. Intracytoplasmic lumens. Lack of mucinous granules and glycocalix	Basal lamina.
Myofibroblastic sarcoma	Spindle shape. Prominent RER. Some thin (6-nm) and peripherally located filaments with focal densities. Fibronexus junction (+/−).	No basal lamina. Abundant matrix with collagen, proteoglycans, and glycosaminoglycans. Fibronectin.
Osteosarcoma	Scalloped or villus-like cell surface. Abundant and dilated RER. Large Golgi apparatus. Abundant glycogen.	Hydroxyapatite deposits on collagen fibers (osteoid) (+/−).
Paraganglioma	Clusters of cells. Round, dense-core granules. Prominent Golgi apparatus. Interweaving cytoplasmic processes. Paranuclear filaments (+/−). Sustentacular (Schwann-like) cells with filaments at the periphery of cell clusters.	Basal lamina surrounding cell clusters.
Parathyroid carcinoma	Islands of cells. Intercellular junctions. Interdigitation of lateral membranes. Dense-core secretory granules. Variable glycogen and cell organelles (RER, SLE, mitochondria, Golgi). Occasional clusters of oncocytic cells.	Basal lamina surrounding cell clusters.
Perineuroma	Whorls of slender cells with bipolar cytoplasmic processes. Pinocytotic vesicles. Scant organelles.	Discontinuous basal lamina. Collagen.
Pheochromocytoma	Clusters of polygonal cells. Large, pleomorphic, dense-core granules (sometimes clear or partially filled). Prominent Golgi apparatus. No significant number of sustentacular cells.	Basal lamina surrounding cell clusters. Many small blood vessels.
Plasmacytoma	Abundant rough endoplasmic reticulum. Membrane-bound dense bodies (+/−). Intercellular junctions (+/−). Eccentric nucleus. Paranuclear area with Golgi apparatus, centriole, mitochondria.	No basal lamina. Amyloid (+/−).
Rhabdomyosarcoma	Thick (15-nm) myosin filaments. Z-band formations. Sarcomeres. Thin (6-nm) filaments. Glycogen. Mitochondria (+/−).	Incomplete basal lamina. Collagen.
Schwannoma	Long intertwining processes. Variable number of mitochondria, RER, lysosomes. Intermediate filaments.	Basal lamina. Collagen in matrix.
Seminoma	Close, appositioned, round to polygonal cells. Intercellular junctions. Large, euchromatic nucleus. Prominent nucleoli. Abundant glycogen. Variable number of organelles; mainly free ribosomes.	Basal lamina (+/−).
Sertoli cell tumor	Polygonal cells. Intercellular junctions. Indented nuclei. Junctional complexes. Interdigitating lateral cell membranes. Abundant SER. Lipid droplets. Mitochondria with tubular cristae. Secondary lysosomes.	Basal lamina. Collagenous matrix.
Squamous cell carcinoma	Desmosomes. Keratohyalin granules. Tonofibrils.	Basal lamina.

(+/−) = Feature not present in all tumors or cells.

(−/+) = Feature rarely observed.