APR 14, 2015 08:18 AM PDT

In the Sea, Deadly Form of Leukemia is Catching

WRITTEN BY: Judy O'Rourke
Outbreaks of leukemia that have devastated some populations of soft-shell clams along the east coast of North America for decades can be explained by the spread of cancerous tumor cells from one clam to another. Researchers call the discovery, reported in the Cell Press journal Cell on April 9, 2015, "beyond surprising."

"The evidence indicates that the tumor cells themselves are contagious-that the cells can spread from one animal to another in the ocean," says Stephen Goff, Howard Hughes Medical Institute and Columbia University. "We know this must be true because the genotypes of the tumor cells do not match those of the host animals that acquire the disease, but instead all derive from a single lineage of tumor cells."
These are soft-shell clams (Mya arenaria) from a seafood market in New York that are sitting on the lab bench while their hemolymph is checked for the presence of neoplastic cells.
In other words, the cancer that has killed so many clams all trace to one incidence of disease. The cancer originated in some unfortunate clam somewhere and has persisted ever since as those cancerous cells divide, break free, and make their way to other clams.

Only two other examples of transmissible cancer are known in the wild. These cancers include the canine transmissible venereal tumor, transmitted by sexual contact, and the Tasmanian devil facial tumor disease, transmitted through biting.

In early studies of the cancer in clams, Goff and his colleagues found that a particular sequence of DNA (which they named Steamer) was found at incredibly high levels in leukemic versus normal clam cells. While normal cells contain only two to five copies of Steamer, cancerous cells can have 150 copies. The researchers at first thought that this difference was the result of a genetic amplification process occurring within each individual clam.

But when first author of the study Michael Metzger analyzed the genomes of cancer cells collected in New York, Maine, and Prince Edward Island, he discovered something else entirely. The cancerous cells they'd collected from clams living at different locations were nearly identical to one another at the genetic level. They were clones.

"We were astonished to realize that the tumors did not arise from the cells of their diseased host animals, but rather from a rogue clonal cell line spreading over huge geographical distances," Goff says.

The result shows that the cells can survive in seawater long enough to reach and sicken a new host. It is not yet known whether the soft-shell tumor can spread to other molluscs, or whether there are mechanisms that recognize the malignant cells as foreign invaders and attack them.

Goff says there is plenty they don't know about this cancer, including when it first arose and how it spreads from one clam to another. They don't know what role Steamer played in the cancer's origin, if any. And they don't know how often these sorts of cancers might arise in molluscs or other marine animals.

But, the researchers say, the findings do suggest that transmissible cancers are more common than anyone suspected.

"Natural horizontal transmission of cancer between individuals has been considered a rare phenomenon, restricted to two exceptional cases in mammals," the researchers wrote. "Our finding of the horizontal transmission of a clonal clam leukemia extends the phenomenon to the marine environment, and demonstrates that this mechanism is more widespread in nature than previously supposed."

The article is "Horizontal Transmission of Clonal Cancer Cells Causes Leukemia in Soft-Shell Clams."

[Source: Cell Press]
About the Author
  • Judy O'Rourke worked as a newspaper reporter before becoming chief editor of Clinical Lab Products magazine. As a freelance writer today, she is interested in finding the story behind the latest developments in medicine and science, and in learning what lies ahead.
You May Also Like
SEP 20, 2018
Genetics & Genomics
SEP 20, 2018
Liquid Phase Separation may Play a Role in Cancer
Not all liquids mix, like oil and water; the phenomenon is called liquid-liquid phase separation. We're learning more about its role in cells....
OCT 06, 2018
Cell & Molecular Biology
OCT 06, 2018
Risks Posed by the Keto Diet
It seems there is no shortage of diet trends, although we've moved on from Atkins and South Beach and into the world of Paleo and keto....
OCT 22, 2018
Videos
OCT 22, 2018
Mad Cow Disease Identified in Scottish Cow
Stringent detection systems appear to be working, but cases still happen....
NOV 12, 2018
Microbiology
NOV 12, 2018
Some Bacteria Gain Resistance Even Without Exposure to Antibiotics
Most bacteria are harmless, some are even beneficial to us. But some of the dangerous ones pose a real threat to public health....
NOV 13, 2018
Microbiology
NOV 13, 2018
How the Microbiome, Fiber, and Heart Health are Linked
High-fiber diets are linked to better health, including healthier hearts and arteries, but why?...
NOV 14, 2018
Cell & Molecular Biology
NOV 14, 2018
Understanding Left-Right Dominance in the Brain
There are many common misconceptions about science, one of which is the belief that someone can be called right- or left-brained....
Loading Comments...