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Study Finds That a Type of Cancer in Dogs Is Contagious
Scientists in England have gathered definitive evidence that a kind of cancer in dogs is contagious -- a peculiar exception to the age-old medical wisdom that you can't "catch" cancer.
Although no human cancer is known to spread naturally from person to person, the finding of such a disease in dogs -- and emerging evidence that a different contagious cancer is spreading among marsupials in Tasmania -- is a reminder, scientists said, that under the rules of evolution, DNA will try anything to perpetuate itself.
...Peyton Rous, 30-year-old research worker at the Rockefeller Institute ...prepared cell-free filtrates from a malignant connective tissue tumour - a sarcoma - that appeared spontaneously in a hen and inoculated it on healthy chickens. Surprisingly enough, the recipients developed tumours of the same type as seen in the original animal. The disease-causing agent present in the filtrate, known nowadays as the Rous sarcoma virus No. 1, could be propagated by serial passage through chickens or fertilized eggs. ...Rous continued his work and showed that even other hen tumours, originating from such tissues as bone, cartilage or blood vessels, could be transmitted by cell-free filtrates. It was remarkable that after inoculation every filtrate reproduced its own original tumour type with great fidelity.
...Rous' findings concerning tumour progression were rapidly confirmed in many experimental systems. On the other hand, his virus theory was received with much skepticism. The notion that virus diseases must be infectious and cancer not due to infectious processes was so deeply ingrained that there was a tendency to explain all virus tumours as strange exceptions. The Rous sarcomas were regarded as bird tumours, of no importance for mammals; the Shope papilloma was a mammalian tumour but of benign nature; and when Bittner discovered in the 1930's a milk-transmitted virus causing breast cancer in mice, it was generally believed that this virus was of minor importance, in comparison with the genetic and hormonal factors that were known to play a rôle in the genesis of this particular tumour.
The situation changed radically in the 1950's. The study of tumour viruses is a central area of modern cancer research. Two developments are responsible for this remarkable change. ... Since 1960 more than a dozen new tumour virus types have been isolated. It was established, furthermore, that tumour viruses could change normal to cancer cells in the test tube after a very short time of contact. This opened the way for direct studies on cancerous transformation of human cells, an approach previously hidden behind the walls of the living organism. Remarkably enough, it could be shown that Rous' own virus, previously regarded as lacking any importance for mammals, induces cancer under certain conditions in many different mammalian species and may even transform human cells in test tube cultures. It took almost half a century for Rous' discovery to advance to its dominant place in modern experimental cancer research.