Science Chats Forum

Laura · #1 08-06-2008, 05:15 PM

The rest of the article said that transmisable tumors have been seen in humans, too
from Harper's magazine:
http://harpers.org/archive/2008/04/0081988

Quote:

Contagious cancer: The evolution of a killer

By David Quammen
During the early months of 1996, not long before Easter, an amateur wildlife photographer named Christo Baars made his way to the Australian island-state of Tasmania, where he set up camp in an old airport shack within the boundaries of Mount William National Park. Baars’s purpose, as on previous visits, was to photograph Tasmanian devils, piglet-size marsupials unique to the island’s temperate forests and moors. Because devils are nocturnal, Baars equipped his blind with a cot, a couple of car batteries, and several strong spotlights. For bait he used road-kill kangaroos. Then he settled in to wait.
The devil, known to science as Sarcophilus harrisii, lives mostly by scavenging and sometimes by predation. It will eat, in addition to kangaroo meat, chickens, fish, frogs, kelp maggots, lambs, rats, snakes, wallabies, and the occasional rubber boot. It can consume nearly half its own body weight in under an hour, and yet—with its black fur and its trundling gait—it looks like an underfed bear cub. Fossil evidence shows that devils inhabited all of Australia until about 500 years ago, when competition with dingoes and other factors caused them to die out everywhere but in Tasmania, which dingoes had yet to colonize. More recently, Tasmanian stockmen and farmers have persecuted devils with the same ferocity directed elsewhere at wolves and coyotes. The devils’ reproductive rate, opportunistic habits, and tolerance for human proximity, however, have allowed localized populations to persist or recover, and at the time of Baars’s 1996 visit, their total number was probably around 150,000.
On his earlier visits, Baars had seen at least ten devils every night, and they were quick to adjust to his presence. They would walk into his blind, into his tent, into his kitchen, and he could recognize returning individuals by the distinctively shaped white patches on their chests. This trip was different. On the first night, his bait failed to attract a single devil, and the second night was only a little better. He thought at first that maybe the stockmen and farmers had finally succeeded in wiping them out. Then he spotted a devil with a weird facial lump. It was an ugly mass, rounded and bulging, like a huge boil, or a tumor. Baars took photographs. More devils wandered in, at least one of them with a similar growth, and Baars took more pictures. This was no longer wildlife photography of the picturesque sort; it was, or anyway soon would become, forensic documentation.
Back in Hobart, Tasmania’s capital, Baars showed his pictures to Nick Mooney, a veteran officer of Tasmania’s Parks and Wildlife Service who has dealt with the devil and its enemies for decades. Mooney had never seen anything like this. The lumps looked tumorous, yes—but what sort of tumor? Mooney consulted a pathologist, who suggested that the devils might be afflicted with lymphosarcoma, a kind of lymphatic cancer, maybe caused by a virus passed to the devils from feral cats. Such a virus might also be passed from devil to devil, triggering cancer in each.
More evidence of contagion began to accumulate. Three years after Baars shot his photographs, a biologist named Menna Jones took note of a single tumor-bearing animal, something she had not seen before. Then, in 2001, at her study site along Tasmania’s eastern coast, her traps yielded three more devils with ulcerated tumors. That really got her attention. She euthanized the animals and brought them to a lab, where they became the first victims to be autopsied by a veterinary pathologist. The “tumors” (until then the term had been only a guess or a metaphor) did seem to be cancerous malignancies, but not of the sort expected from a lymphosarcoma- triggering virus. This peculiarity raised more questions than it answered. Tasmanian devils in captivity were known to be quite susceptible to cancer, at least in some circumstances, possibly involving exposure to carcinogens. But the idea that the cancer itself was contagious seemed beyond the realm of possibility. And yet, during the following year, Menna Jones charted the spread of the problem across northern Tasmania. Nick Mooney, meanwhile, had done some further trapping himself. At a site in the northern midlands, he captured twenty-three devils, seven of which had horrible tumors. Shocked and puzzled, he remembered the Baars photos from years earlier.
Further trapping (more than a hundred animals, of which 15 percent were infected) showed Mooney what Jones had also seen: that the tumors were consistently localized on faces, filling eye sockets, distending cheeks, making it difficult for the animals to see or to eat. Why faces? Maybe because devils suffer many facial and mouth injuries—from chewing on brittle bones, from fighting with one another over food and breeding rights, from the rough interactions between male and female when they mate. The bigger tumors were crumbly, like feta cheese. Could it be that tumor cells, broken off one animal, fell into the wounds of another, took hold there, and grew? This prospect seemed outlandish, but the evidence was leading inexorably to a strange and frightening new hypothesis: the cancer itself had somehow become contagious.
Under ordinary circumstances, cancer is an individuated phenomenon. Its onset is determined partly by genetics, partly by environment, partly by entropy, partly by the remorseless tick-tock of time, and (almost) never by the transmission of some tumorous essence. It arises from within (usually) rather than being imposed from without. It pinpoints single victims (usually) rather than spreading through populations. Cancer might be triggered by a carcinogenic chemical, but it isn’t itself poisoning. It might be triggered by a virus, but it isn’t fundamentally viral. Cancer differs also from heart disease and cirrhosis and the other lethal forms of physiological breakdown; uncontrolled cell reproduction, not organ dilapidation, is the problem.
Such uncontrolled reproduction begins when a single cell accumulates enough mutations to activate certain growth-promoting genes (scientists call them oncogenes) and to inactivate certain protections (tumor suppressor genes) that are built into the genetic program of every animal and plant. The cell ignores instructions to limit its self-replication, and soon it becomes many cells, all of them similarly demented, all bent on self-replication, all heedless of duty and proportion and the larger weal of the organism. That first cell is (almost always) a cell of the victim’s own body. So cancer is reinvented from scratch on a case-by-case basis, and this individuation, this personalization, may be one of the reasons that it seems so frightening and solitary. But what makes it even more solitary for its victims is the idea, secretly comforting to others, that cancer is never contagious. That idea is axiomatic, at least in the popular consciousness. Cancer is not an infectious disease. And the axiom is (usually) correct. But there are exceptions. Those exceptions point toward a broader reality that scientists have begun to explore: Cancers, like species, evolve. And one way they can evolve is toward the capacity to be transmitted between individuals.
Devil tumor isn’t the only form of cancer ever to achieve such a feat. Other cases have occurred and are still occurring. The most notable is Canine Transmissible Venereal Tumor (CTVT), also called Sticker’s sarcoma, a sexually transmitted malignancy in dogs. Again, this is not merely an infectious virus that tends to induce cancer. The tumor cells themselves are transmitted during sexual contact. CTVT is widespread (though not common) and has been claiming dogs around the world at least since a Russian veterinarian named M. A. Novinsky first noted it in 1876. The distinctively altered chromosome patterns shared by the cells of CTVT show the cancer’s lineal continuity, its identity across space and through time. Tumor cells in Dog B, Dog C, Dog D, and Dog Z are more closely related to one another than those cells are to the dogs they respectively inhabit. In other words, CTVT can be conceptualized as a single creature, a parasite (and not a species of parasite, but an individual), which has managed to spread itself out among millions of different dogs. Research by molecular geneticists suggests the tumor originated in a wolf, or maybe an East Asian dog, somewhere between 200 and 2,500 years ago, which means that CTVT is probably the oldest continuous lineage of mammal cells presently living on Earth. The dogs may be young, but the tumor is ancient.
Unlike devil tumor—now known as Devil Facial Tumor Disease, or DFTD—CTVT is generally not fatal. It can be cured with veterinary surgery or chemotherapy. In many cases, even without treatment, the dog’s immune system eventually recognizes the CTVT as alien, attacks it, and clears it away, just as our own immune systems eventually rid us of warts.

carlodalid1 · #2 05-31-2010, 12:00 PM

Are there cases of cancer transmission in humans through physical contact? I have not heard of any case yet. I just want to make sure. On the other hand, cancer is present in every human being. It will become harmful if the number of cancer cells in the body go beyond the normal number of cancer cells the body can manage. Based on the book I have read, cancer cells feed on protein thus, meat eaters are more prawn to the disease. Eating fruits can vegetables can help the body stop the spread of cancer cells.

Laura · #3 07-20-2010, 07:00 AM

Before my grandmother died of cancer (non-Hodgkins' lymphoma) in 1978, the hospital that was treating her tried some experiemental techniques based on those very ideas. #1 They took blood samples from all adult members of the family, #2 they tried introducing some of my grandfather's antibodies into her system. This didn't "work", but perhaps with earler detection and the general fine tuning that is available these days, a similar approach might. Funny thing, it was only a few years after my grandmother died from cancer (though it may really have been the chemotherapy/radiation that killed her) that my grandparents' _dog_ died from cancer as well!
(My grandfather has always been quite robust health-wise and is still with us today).

Science Chats Forum

Search

Navigation

Sponsored links

Cool sites