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Poor Devils: Critters' fights transmit cancer

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9:56am, February 1, 2006
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A fatal cancer afflicting Tasmanian devils passes from one of the small marsupials to another when they bite each other, rather than being transmitted via a virus, a new study suggests. The disease is the first cancer known to spread directly from scratch to scratch.

The whirling cartoon version of a Tasmanian devil may not look much like the furry reality, but it does capture the creature's legendary fierceness.

"They're always squabbling and fighting. They don't share food, and their [mating] foreplay isn't much better," says cytogeneticist Anne-Maree Pearse of Tasmania's Department of Primary Industries, Water and Environment in Kings Meadows. "They bite each other around the face and mouth."

That behavior may have deadly consequences, Pearse says. The disease appeared in the 1990s and by 2004 had spread across more than half the Australian island. It produces lesions that soon develop into large tumors on the face and neck, preventing the animal from eating. Within 6 months of the lesions' appearance, most devils die of starvation.

Pearse and her colleagues searched for a virus that might transmit the disease, but they came up empty. "It occurred to me that there didn't necessarily have to be a virus if the [cancer] cells themselves could be transmitted," Pearse says.

To learn more about the tumor cells, she and her colleagues investigated the animals' chromosomes. They found identical complex chromosomal anomalies in the cancer cells of all of the 11 afflicted animals studied. That uniformity wouldn't occur if the disease were caused by a virus, Pearse says. In virus-induced cancers, chromosomes begin mutating from a common point and then evolve through several stages, resulting in many different complex chromosomal rearrangements.

But rearrangements in the devils' tumors, though highly complex, were identical, suggesting that all the tumors are the work of a single rogue cell line grafted onto the animals, the team reports in the Feb. 2 Nature.

The clincher, Pearse adds, was that the researchers found an abnormal chromosome in one animal's nontumorous cells but not in its tumor cells. "That meant the tumor couldn't have arisen from [the animal's] own tissues," she says.

Since Pearse and her colleagues finished the original study, they've analyzed chromosomes in 15 more animals, and all the tumors have shown the same distinctive anomalies. This result bolsters the theory that one rogue cell line was the original infective agent, Pearse says.

Though this is the first documented instance of trauma-transmitted cancer cells, scientists know of one similar case: a nonlethal venereal sarcoma that passes between dogs during genital contact. In that example, too, the tumors' chromosomal defects are similar from dog to dog.

Wildlife biologist Menna Jones of the University of Tasmania in Hobart says the new paper presents "sound, plausible, impeccable science." If direct contact transmits the cancer between devils, she says, the most effective strategy to control the disease may be to quarantine infected animals. As part of Tasmania's Devil Disease Project, Jones and several collaborators are already testing this strategy on parts of the island. Results so far are encouraging, she says.

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