The role of electron microscopy in the determination of tumour histogenesis.

In the majority of cases the histogenesis and classification of tumours can be unequivocally established by light microscopy, but in some instances the diagnosis remains ambiguous even after special staining techniques have been employed. So wide and varied are the situations in which the electron microscope can help establish a diagnosis that it is impossible to even mention them all in the brief time available. I will therefore present only a brief description of the manner in which one can resolve with the electron microscopy some well known diagnostic problems. This includes distinguishing: (1) an anaplastic carcinoma from a sarcoma; (2) an amelanotic melanoma from other tumours; (3) APUDomas from other tumors; (4) myosarcomas from other tumours; and (5) Ewing's tumour, neuroblastoma and lymphoma from each other.