Study Reveals Pathway for Contagious Clam Cancer

Although rare, some cancers can be transmitted from one organism to another. Scientists have observed them in Tasmanian devils, dogs, and several shellfish species.

A team of researchers and students from Bigelow Laboratory for Ocean Sciences recently helped confirm that cancer cells from the soft-shell clam Mya arenaria could be spread through seawater and likely be infectious. The research marks some of the first steps to better understand contagious cancer's dynamics and mitigate its spread to support the shellfish industry.

“We now know that this disease is transmitted through the water, so we have a better idea how long the cells remain active in the environment and infect clams,” said Senior Research Scientist José Antonio Fernández Robledo, a co-author of the paper. “We can use these results to study the prevalence of the disease and what the cells are doing in the water.”

The results were published in the journal Pathogens, led by Rachael Giersch and Michael Metzger from the Pacific Northwest Research Institute. The team also included two undergraduate students, Satyatejas G. Reddy and María José Orellana Rosales, who worked at Bigelow Laboratory as interns in the National Science Foundation’s Research Experience for Undergraduates program in 2021.

Bivalve transmissible neoplasia, or BTN, has been reported in eight different bivalve species. Although the scientists do not believe it poses a human health risk, it could have other consequences for people and the environment.

“Clams are a valuable economic resource and part of the Maine working waterfront,” said Senior Research Scientist Pete D. Countway, also a co-author of the paper. “They are also a valuable resource for the environment – bivalves help clear and filter the water. If their populations are compromised by disease, there could be downstream ecosystem effects that we're not going to like.”

The team partnered with a local clam harvester to study clams in three locations around Maine and find DNA evidence of BTN cancer cells in the water. They also used a molecular PCR test, similar to those used for detecting the virus that causes COVID-19, to look for evidence of the cancer both in the environment and in saltwater tanks holding infected clams.

Researchers found traces of the cancer cells in both sources, although the occurrence in nature was low. The results show the infectious cells can be released from infected clams and survive in saltwater, but further research is needed to determine how big of a role that route plays in its spread. The scientists hope to build on this work, use models to forecast infections, and help fishery managers mitigate the disease.

“If we're able to understand how the disease moves, we may be able to create a tool that enables managers to identify and isolate infected areas,” Fernández Robledo said. “Maybe then we can break the transmission and essentially get rid of the disease.”