Analysis of osteoid-forming activity of human osteosarcoma implanted into nude mice.

Thirty cases of human osteosarcoma were transplanted subcutaneously in BALB/c nude mice. Twenty-four tumours survived in animals and showed the histopathology of the original tumours. Growth of transplantable tumours was closely related to the amount of osteoid tissue and tumours with predominant osteoid tissue showed slow growth. Tumours whose osteoid-forming activity tended to diminish or disappear were likely to fail early during serial transplantation. Two osteosarcoma (SU and ISHI) were established into permanent transplantable strains and were maintained in nude mice for more than three years. These two strains showed striking differences in their growth capacity; SU grew rapidly and frequently formed pulmonary tumours after tail vein injection of tumour cells. Histologically, ISHI osteosarcoma cells continue to form osteoid tissue, whereas SU cells showed anaplastic changes and lost osteoid-forming activity. Alkaline phosphatase and Lactate Dehydrogenase (LDH) activities of tumour tissue were lower in ISHI than SU, and significant elevation of the relative value of Fraction III of LDH isozyme has been demonstrated in SU, and Fraction IV in ISHI. On this basis, the authors discuss the relation between the amount of osteoid formation or LDH isozyme patterns and the malignant potential of human osteosarcoma.