Scientists have discovered that cancers have been spreading for centuries among shellfish — a revolutionary reveal that could change the way cancer is treated.
According to a study recently published in the peer-reviewed journal Nature, researchers at the UK’s Wellcome Sanger Institute, and the Universidade de Santiago de Compostela in Spain collaborated with experts in several other countries to use DNA sequencing to examine how certain, ancient cancers have been spreading silently among cockles since ancient times.
Cockles are a species of edible saltwater clam which belong to one of the oldest groups of animals on the planet.
Contagious cockle cancers are known as bivalve transmissible neoplasia (BTN). The disease is spread from one cockle to the next through seawater, which passes living cancer cells, which multiply and replicate in their host — like leukemia — before escaping to attack others.
This mode of contagion has been found among species of Tasmanian devils (which transmit cancer cells when they bite each other), dogs (which spread cancer cells through mating) and very rarely in humans (a few cases of cancer being passed to children during pregnancy have been reported).
Collecting around 7,000 cockles at 36 locations from 11 countries including Spain, Portugal, the UK, Ireland, and Morocco, the team was able to find two different types of BTN.
“We clarified the existence of two independent transmissible cancers, and we suspect that there are many more different types out there,” Dr Alicia Bruzos, co-first author, said in a statement.
“Having a wider view of the different types of transmissible cancers can give us more insight into the conditions necessary for tumors to evolve and survive long-term.”
The team found that these cockle tumors are highly genetically unstable and contained different numbers of chromosomes, an unusual occurrence for cancers.
Dr Daniel Garcia-Souto, co-first author, said: “Our study showed that the cells in these cockle tumors contain highly variable amounts of genetic material, which is very unusual compared to other types of cancer.”
“These cancers have been undergoing extreme chromosomal changes and continuous genetic reorganization, probably for hundreds or thousands of years, which challenges the theory that cancers require stable genomes to survive long-term.”
The finding suggests that these cancers are unlike any other transmissible cancer in animals, as a stable genome is not necessary for these transmissible cancers to survive.
Discovering how these cancerous cells are able to tolerate this instability could help experts find new ways of approaching the treatment of cancer in humans.
The researchers also identified a number of cockles that had unexpectedly been co-infected by cells from both types of cancers at the same time.
“Understanding more about the origins and evolution of cockle transmissible cancers, and how their cells interact with cockle cells and the marine environment, could help protect animal populations in the future, while providing insight into how cancers can survive for thousands of years as marine parasites,” Dr Adrian Baez-Ortega, joint senior author, explained.