Scientists discover ancient cancer that can SPREAD like a virus among shellfish – as they warn ‘there could be many more transmissible types out there’
A transmissible cancer that spreads like a virus may sound like part of the plot of an apocalyptic movie, but it’s a reality in the animal kingdom.
A study published last week discovered two strains of an ancient form of leukemia-like cancer that has spread silently among shellfish for centuries.
The transmissible tumor cells, like microscopic bacteria, swim freely in the water before being ingested by mussels, multiplying and replicating within their host before escaping and attacking others.
This type of spread is similar in Tasmanian devils, which pick up cancer cells when they bite and fight each other, and in dogs, which pass them on from each other through mating.
Infectious cancer is considered accidental in nature and occurs in a limited number of animal species. But the latest discovery in shellfish suggests that there are other cancers of this type that pose a potential threat to humans.
As far as scientists know, cancer can only be transmitted to humans in extremely rare cases. For example, there have been a handful of cases of Mothers pass cancer on to their babies during pregnancy.
Researchers from the United Kingdom, Spain, France, Poland, Belgium, Portugal, Norway and Korea sampled nearly 7,000 cockles and genetically sequenced 61 cockle tumors at 36 sites in 11 countries. They were then able to detect two different strains of a transmissible leukemia cancer
Researchers sequenced genetic data from cockles, a clam-like mollusc, and tumor cells inside them that had invaded their gills and circulated through their bloodstream before killing their hosts and traveling through the water in search of their next victims
The latest research sequenced tumor genes sampled from 7,000 cockles, edible molluscs similar to mussels, between 2016 and 2021 at three dozen sites in 11 countries, including Spain, Portugal, Britain, Ireland and Morocco.
Specifically, the type of cancer is bivalve-transmitted neoplasm (BTN), which invades through the gills and spreads throughout the mollusk’s circulatory system.
British and European researchers led by Dr. Adrian Baez-Ortega, a biologist at Britain’s Wellcome Sanger Institute, mapped the DNA of whole cancer cells, as well as the animals that harbor them, to pinpoint the hundreds of thousands of genetic mutations that have occurred over hundreds of years.
By tracking the genetic transformation of the cancer tumor cells, the researchers discovered wild inconsistencies that suggest this type of cancer in mollusks is unlike any other transmissible cancer in animals.
Some tumor cells had more or fewer chromosomes than others, due to generations of cell division and other abnormal changes in the cancer cells’ genetics.
While a normal cockle cell has 38 chromosomes, they found tumor cells with only 11 and even 354 chromosomes.
This type of chromosomal instability is believed to have helped the BTN lineage, which researchers say originated from a single mutant cell within a single clam, survive centuries of genetic chaos.
Dr. Alicia Bruzos, co-author and molecular researcher at the Universidade de Santiago de Compostela in Spain, said: “We have clarified the existence of two independent transmissible cancers and suspect that there are many more different types.”
“A broader look at the different types of transmissible cancers can give us more insight into the conditions required for tumor development and long-term survival.”
Their finding – that an ancient cancer can thrive in an animal population despite years of genetic reworking – contradicts the common understanding that cancer cells can only reproduce, mutate and spread within a larger organism whose genetic makeup has undergone relatively infrequent DNA changes over time.
According to Dr., there would be too many changes in the environment in which the cancer lives. Baez-Ortega typically prove fatal to the cancer cell.
Aside from molluscs, the only other animals found to be affected by transmissible cancer are dogs, which transmit it through mating and biting, and Tasmanian devils, which pass on tumor cells growing on their faces when other devils pass them on bite.
But in these species, their complete sets of chromosomes have remained virtually unchanged over time – even transmissible cancer in dogs, which first appeared 11,000 years ago.
Dr. Daniel Garcia-Souto, another co-author and researcher at the Universidade de Santiago de Compostela, said: “Our study showed that the cells in these cockle tumors contain very different amounts of genetic material, which is significant compared to other types of tumors is very unusual.” Cancer.
Tasmanian devils are one of two other species known to be susceptible to infectious cancer, along with domesticated dogs. The tumors are growing on their otherwise adorable faces. When two devils fight, one of them bites the tumor on one of their faces. The tumor cells then enter the other devil through wounds on his body
“These cancers have likely been undergoing extreme chromosomal changes and continuous genetic reorganization for hundreds or thousands of years, challenging the theory that cancer requires stable genomes for long-term survival.”
The fact that the transmissible neoplasm spreads like a bacterium in water and infects the gills of molluscs suggests that there may be undiscovered rules governing the way cancer invades the human body.
Dogs and Tasmanian devils have relatively small gene pools, which allows cancers to spread more widely because the hosts remain largely unchanged. However, thanks to a long history of human migration and evolution that has equipped humans with a cancer-fighting immune system, human DNA is far more diverse.
But recent findings from the Wellcome Sanger Institute suggest that even genetically distinct species like humans could one day see some versions of a transmissible leukemia-like cancer that currently affects mollusks.
There have been some cases of transmissible cancers in humans, but only in medical or research settings when the skin’s protection has been breached. For example, a surgeon removing a tumor from a patient accidentally cut his hand, and five months later a tumor grew there that was genetically linked to his patient.
The team’s results were published in the journal Natural cancer.