The ultrastructure of skeletal haemangiosarcomas induced in mice by strontium-90

The commonest skeletal tumour occurring in male CBA and C3H mice injected with 7--13 muCi 90Sr (per mouse) at Harwell was diagnosed with the light microscope as haemangiosarcoma. On the other hand, Nilsson, using male CBA mice injected with similar amounts of 90Sr, recorded the predominant tumour as fibroblastic osteosarcoma. To resolve the apparent discrepancy, samples of non-osteogenic tumours induced by 90Sr at Harwell were examined with the electron microscope and their ultrastructure compared with that described for fibroblastic osteosarcoma by Nilsson. The tumours diagnosed as haemangiosarcoma at Harwell showed ultrastructural features not observed in the fibroblastic osteosarcomas. Vasoformation was marked, the vascular channels varying in shape, size and in the character of their lining cells. Some vascular channels were lined by cuboidal cells, crowded together, and surrounded by a basement membrane. Others were lined by an attenuated endothelium and often formed networks. The tumour cells showed great variation in shape, size and ultrastructure and were sometimes enclosed by a basement membrane. Thus the ultrastructure of the tumours described in this report supports the diagnosis of haemangiosarcoma, rather than fibroblastic osteosarcoma. The question of whether these haemangiosarcomas truly originate from vascular endothelium, or are mimics, is discussed.