Electron microscopy (EM) for the diagnosis of tumor has largely been replaced by immunohistochemistry (which may be replaced by gene arrays in the future), but occasionally can provide useful information.
Indications for electron microscopy - further categorize:
(1) poorly differentiated sarcomas
(2) small cell tumors
(3) undifferentiated tumors
(4) metastatic tumor of unknown primary
(5) clear cell tumor of the retroperitoneum
(6) tumors of the anterior mediastinum
(7) head and neck tumors
(8) tumors of the central nervous system
(9) tumors with negative or inconclusive immunohistochemical profiles
(10) pleural or peritoneal tumors
Indications for electron microscopy - identify specific cell types:
(1) neuroendocrine cells
(2) melanocytes (melanoma)
(3) plasma cell
(4) mesothelial cells (mesothelioma)
Tumor
Diagnostic Feature
granular cell tumor
lysosomes
Langerhans cell
Birbeck granules in cytoplasm
leiomyosarcoma
smooth muscle filaments
melanoma
melanosomes
meningioma
undulating cytoplasmic extensions
mesothelioma
microvilli
nerve sheath tumor
mesoaxon
neuroendocrine tumor
granules
plasma cells or lymphocytes
immunoglobulin crystalline deposits
squamous cells
desmosomes and tonofilaments
steroid-producing tumors
mitochondria with tubular cristae; abundant endoplasmic reticulum
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