1. That viruses may be involved in the causation of human tumours has long been suspected but not yet proved. The discovery that osteogenic sarcoma can be induced by viral agents in mice and hamsters makes the proposition that human sarcomas may also have a viral origin basically tenable on presently available evidence. In order to distinguish between passengers and causative agents it will probably be necessary to demonstrate antigenic cross-reactivity in tumours of similar type collected from different geographical areas, and the oncogenicity in subhuman primates of extracts containing virus from human tumours. Such information is likely to become available in the next few years.

2. The demonstration of tumour-specific immune reactions in an increasing number of patients with various forms of neoplasm, including skeletal sarcomas, and the correlation of these reactions with the clinical status of the disease sustains the hope that eventually immunotherapy may contribute to the control of cancer in man.

3. Animal experiments have revealed that the potentiation of immune responses may lead to the elimination of small foci of neoplastic cells. The role of immunotherapy in the treatment of cancer may therefore be as an adjunct to surgery, radiotherapy and chemotherapy (Alexander 1968). Once the primary tumour has been removed it may be possible to employ immunotherapeutic measures to destroy the relatively few remaining cells that give rise to late metastases; this is particularly apposite to juvenile osteosarcoma.