The first study investigated the in-vitro release of antimitotics included in acrylic cement. After confirming that this release does actually occur, starts rapidly and is maintained over a prolonged period, two further studies were then carried out in vivo: one in dogs suffering from spontaneous osteosarcoma, in order to investigate the release of the antimitotic from the cement into the plasma, the systemic safety and the local activity of the antimitotic-loaded cement following exeresis of the neoplasm.

The second study was conducted in laboratory rats with implanted osteosarcomas. This type of tumour was used so that a large number of animals with tumours could be studied and divided into uniform groups. Under these experimental conditions, it was possible to monitor the progress of the tumours left in situ as well as the histopathological changes brought about by the local action of antimitotics released from implants.

To investigate the release of MTX from a block of acrylic cement implanted into the tissues, cubic test pieces were placed in 32 ml of physiological saline, which was changed every day. The concentration in the elution fluid was measured before each change. These test pieces were made from a mixture of 500 mg methotrexate powder, 46.5 g of polymer, and 20 ml of monomer, poured into 2 cm cubic moulds. Each cube weighed about 13 g and contained approximately 100 mg of methotrexate. Methotrexate elution was evaluated daily for 15 days and then weekly for 6 months for six specimens, the results being given as an average of the 6.

The release profiles from implants containing 1 % w/w have shown that methotrexate is released more rapidly during the first 2 h and 10 % of the load is released within the first 18 h. The rate of release then slows. Implants immersed in an extraction medium which is changed regularly, continue to release methotrexate for 6 months; the quantities released initially being greater the greater the initial load.

This has been investigated in vivo in dogs with spontaneous sarcoma. We therefore chose an animal with a weight close to that of man, and a spontaneous tumour with an evolution like that of human osteosarcoma, similarly hypervascular because this may influence the diffusion of cisplatine. In experiments at the National Veterinary School of Maisons-Alfort, we used dogs with spontaneous osteosarcoma. This is a malignant tumour [15, 16] with the same aggressive properties as the human type. It affects the very large breeds of dog such as the Saint Bernard (mean weight 70 kg), the mastiff (55 kg) and the boxer (30 kg). It progresses rapidly in the absence of treatment, and death is the rule in a few months [17, 18]. Simple resection of the tumour rapidly leads to local relapse, and even after amputation 85 % of dogs die within 7 months of diagnosis [15, 19, 20]. The loss of substance resulting from the exeresis of the tumour was compensated using freshly prepared methotrexate-loaded cement. The dose of methotrexate received ranged from 1.6 to 16 mg/kg. Two hours after being implanted, plasma levels of methotrexate ranged from 0.08 to 0.02 μmol/l (1 μmol of methotrexate = 0.455 mg). After 24 h, the plasma levels were between 0.1 and 0.02 μmol/l and by the third day were no longer detectable. Toxic effects were observed on day 4 in the 3 animals which had received a dose of more than 200 mg of methotrexate. The other animals, which had received a dose of between 100 and 150 mg, did not display any signs of toxicity. The survival curve of the animals in this group seemed to be better than that of the animals which underwent surgery without adjuvant treatment, where 85 % of the animals had died within 7 months.