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OSTEOSARCOMIA is the most common tumour of bone in the dog although chondrosarcoma, fibrosarcoma, haemangiosarcoma and other less common primary or metastatic tumours of bone also occur. Brodey, Saver and Medway (1963) found that of 50,750 dogs examined between 1952 and 1962 at the University of Pennsylvania Hospital, 152 had bone sarcomas whereas during this same period only 2 dogs with benign bone tumours were observed.Osteosarcoma is more common in the large breeds and it appears that the Great Dane and St. Bernard have the greatest predisposition. The origin is common in the distal radius, proximal humerus and distal tibia but rare in the distal humerus and proximal radius. Tumours occur in other long and in flat bones.There is considerable variation in the speed of growth. Some rapidly growing vascular tumours can destroy a large area of bone in 3 weeks whereas other denser, more cartilaginous tumours may develop over a period of months.Amputation of the affected limb in large breeds is rarely performed in Great Britain and no records of survival are available. A large dog has difficulty in balancing after the removal of a forelimb, and often shows over-extension of the opposite carpus. The development of lung metastases is usually rapid so that euthanasia rather than amputation is recommended. Brodey, Saver and Medway (1963) have described the results of amputations carried out in Pennsylvania on 21 dogs. Most dogs did not die naturally but were killed in the terminal stages of the disease with metastases in the lungs and frequently in other sites. Following amputation 10 dogs were dead within 3 months and a further 8 died between 3 and 7 months. Only 3 dogs lived for longer than 10 months. Knight (1963, personal communication) has treated a small number of cases of osteosarcoma by X-irradiation and while some remarkable histological changes were observed there were no cures and the development of lung metastases was not prevented. Silver (1964), who treated osteosarcomas by X-irradiation or the intra-arterial injection of tritiated " Synkavit " obtained disappointing results. Even in cases where there was relief of pain and reduction in tumour size there was recurrence or metastasis necessitating the destruction of the dog.The treatment of spontaneous tumours in dogs with cytotoxic drugs has been attempted by McCoy, Allison, Crossley and Wannermacher (1956) using MEPA.

AT THE TIME the puppy was bought, at 8-weeks old, a small thickening on the dorsal surface of the head in the occipital region was noticed. Five weeks later the owner reported that the mass was increasing in size and shortly after this it was excised. Recurrence was rapid. E X A M I N A T I O NThe animal was examined at 16 weeks of age and appeared healthy and in good condition. A firm oval mass about 3 . 5~2~7 cm in the subcutaneous tissues was present in thc occipital region (Fig. 1). The scar of the operation 3 weeks previously was present and both scar and skin were freely moveable over the underlying mass. Regional lymph nodes were not palpable and radiographs of the skull and thorax showed no abnormality. Haematological values were within the normal range and serum levels of calcium and phosphorus were normal. Serum alkaline phosphatase was 13 K.A. units which is also normal for a dog of this age. OPERATIONUnder methoxyfhorane anaesthesia the mass was excised using diathermy and taking as wide an incision as possible. As the tumour appeared to be attached to the periosteum of the frontal bone this area of attachment was thoroughly curetted.The wound was washed with 1 % cetrimide, in an attempt to destroy any remaining malignant cells, followed by washing in normal saline. The wound was then closed using vertical mattress sutures of braided nylon. Post-operative oedema was marked and a serosanguinous fluid collected subcutaneously. This was drained off on the fifth post-operative day and thereafter healing was satisfactory.Examination of the dog 34 months after operation showed slight skin thickening only over the site of incision and on radiography the lungs appeared normal. S i x 399

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