By Diana Kenney
The startling discovery of a contagious cancer in steamer clams, published this week in the journal Cell, had its origins at the MBL.
Carol Reinisch began studying a fatal, leukemia-like disease of soft-shell clams (Mya arenaria) at the MBL in the mid-1970s, when it was causing major die-offs among distinct bivalve populations. This week, scientists announced that the disease is a contagious form of cancer that has been transmitted between clam populations from New York to Prince Edward Island, Canada. The study was conducted by Michael Metzger and Stephen P. Goff of Columbia University, Jim Sherry of Environment Canada, and Reinisch.
The soft-shell “steamer” clam, Mya arenaria. Photo by Scott Bennett, MBL
Infectious cancer (or “super metastasis”) is known in only two other instances in nature: as a venereal disease in dogs and as a facial tumor in Tasmanian devils, according to an article about the clam leukemia in Science.
Reinisch, a few years ago, thought the clam disease might be caused by a virus, and she brought it to Goff’s attention. Metzger and Goff, she says, “conducted the truly elegant molecular biology to show the cancer is externally derived.”
Through genetic analysis of numerous sick clams, the team showed that while their cancer cells were nearly identical, the cancer cells did not match the genomes of their host clams. This indicates the cancer cells likely descended from a single, original clam cell “gone rogue,” which then multiplied and spread to nearby clams. How the disease was transmitted is still unknown.
Steamer clams are eaten by human beings and are an important commercial fishery. However, researchers say there is no health risk to humans who eat diseased clams. “Nobody eats them raw. When you steam or boil them, it kills all the cells,” Reinisch says.
Reinisch has studied this clam and bivalve disease for decades because “it’s one of the best and unique models of carcinogenesis in nature that we have,” she says. She carried out research at MBL for more than 30 years, first as a Whitman summer investigator and then, from 1998 to 2005, as a year-round scientist. She moved her lab to the MBL in order to explore Mya arenaria as a model system for cancer. Formerly, she was a Department Chair of Comparative Medicine at Tufts Veterinary School.
Reinisch’s earlier work indicated that the spread of the clam leukemia has an environmental component. “For whatever reason, the [cancer] transmission seems to be easier in stressed areas,” she says. “When we used to collect clams in New Bedford, Mass., we knew exactly where to find the ones with leukemia. The clams in a PCB contaminated site were much more liable to have the disease.”
Currently, Reinisch collaborates with Environment Canada in Burlington, Ontario, and is identifying the range of this transmissible cancer. She has studied bivalves as far north as Alaska and the Arctic and hopes to conduct field research in Antarctica in the coming year.
Metzger, MJ, Reinisch C, Sherry J, and Goff SP (2015) Horizontal transmission of clonal cancer cells causes leukemia in soft-shell clams. Cell 161: 255-263.