Invasion of cartilage by an experimental rat tumor.

The in vivo invasion of cartilage of the xiphisternum by a transplantable malignant rat tumor has been investigated with histochemical methods. Staining of cartilage with toluidine blue was considerably reduced or absent at the edge of the invading tumor. Frequently, matrix staining around chondrocytes close to the tumor was much more intense than that of more remote matrix. This pericellular staining feature was also observed in cartilage from tumorfree animals treated with papain but was absent from those which received an excess of vitamin A. Appreciable inter cellular ß-glucuronidase activity was observed in tumorinfiltrated cartilage, but not in normal cartilage. In chondrocytes, this enzyme was normally observed in small cytoplasmic particles (0.2 to 0.5 n in diameter). In the presence of the established tumor, however, larger stained particles (1.0 to 2.0 ¿u in diameter) were frequently observed. The rate of lysosomal staining for acid phosphatase was unchanged in chondrocytes and fibroblasts of cartilage undergoing early tumor infiltration, but was increased in later cases. These results are interpreted and considered in the light of the proposal that lysosomal acid hydrolases are released from the tumor, and normal cells and their extracel lular activity plays an essential role in malignant invasive growth.