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Invasion of Cartilage by an Experimental Rat Tumor

The Research Department, The Marie Curie Memorial Foundation, Harestone Drive, Caterham, Surrey, England

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 tumor-free animals treated with papain but was absent from those which received an excess of vitamin A. Appreciable intercellular µ-glucuronidase activity was observed in tumor-infiltrated cartilage, but not in normal cartilage. In chondrocytes, this enzyme was normally observed in small cytoplasmic particles (0.2 to 0.5 µ in diameter). In the presence of the established tumor, however, larger stained particles (1.0 to 2.0 µ 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 extracellular activity plays an essential role in malignant invasive growth.

¹ Present address: Strangeways Research Laboratory, Wort's Causeway, Cambridge, England.

Received 12/18/69. Accepted 5/ 7/70.