Electron microscopy is useful for the diagnosis of tumours, which are difficult to diagnose by other techniques such as light microscopy.
Electron microscopy is useful because it can detect distinctive cell structures, which indicate a particular tumour cell type and therefore a particular tumour.
For electron microscopy, small pieces of tissue about 1mm across are removed from the main surgical specimen fixed in formaldehyde, and embedded in a plastic to allow the thin sectioning needed for the electron microscope.
When examined in an electron microscope, features like those in the illustration may be seen. This example is from a neck tumour where light microscopy examinations were unable to distinguish between a lymphoma (a tumour of lymphocytes) and a carcinoma (a tumour of epithelial cells).
In this case, electron microscopy demonstrated dark-staining tonofibrils, and intercellular junctions called desmosomes: both of these organelles are distinctive for epithelial cells, and in this case, therefore, carcinoma, but not lymphoma.
Electron microscopy is also useful for identifying myeloma, the macrophage lesion, Histiocytosis X, mesothelioma, malignant melanoma, carcinoid tumours, nerve-cell tumours such as neuroblastoma, and sarcomas such as fibrosarcoma and rhabdomyosercoma.