Histochemical and electron-microscopic aspects of bone tumor diagnosis

In recent years, histochemistry and electron microscopy have been applied more and more to the investigation of bone tumors. The contributions and limitations of these methods in differential diagnosis are discussed. The levels of glycosaminoglycans in cartilaginous tumors display distinct differences between slow- and fast-growing types. All cartilaginous tumors are poor in phosphatase activity. Demonstration of these enzymes at acid and alkaline pH in bone-forming conditions reveals differences between benign and malignant tumors. Osteosarcomas display a rich activity of both phosphatases in bone-forming and in bone-free regions. Acid phosphatase may play a rôle in the breakdown of the host tissue infiltrated by the tumor. Electron microscopy of bone tumors has brought out some interesting findings. In fibrous dysplasia a particular kind of very fine fibrillar structures was observed besides the regular collagen fibrils. This may indicate retardation of collagen maturation. Cell organelles in benign and malignant bone tumors usually differ quantitatively. They resemble active fibroblasts. In bone- and in cartilage-forming tumors we observed large quantities of microfilaments in the cytoplasm. Nuclear indentations and invaginations probably indicate increased nuclear activity. The intense acid phosphatase activity demonstrated histochemically seems inconsistent with the low number of lysosomes in the cytoplasm of osteosarcoma cells, but other organelles (Golgi apparatus and vesicles) may also contain the enzyme. Virus-like particles have not been observed in human osteosarcomas up to now. Other authors have observed a correlation between the number of cell organelles and the grade of differentiation, but this was not detected in our sample of benign and malignant cartilaginous tumors. Histochemistry and electron microscopy of bone tumors are still in the early stage of material gathering. Some histochemical findings, however, can already be used as diagnostic tools.