April 1st 2021
Most cancers are caused by many complex factors including aspects of the environment, such as toxins and pollutants, and genetic predispositions, such as having the BRCA1 and BRCA2 gene in breast cancer. This complexity makes it challenging to capture all possible factors causing cancer in traditional laboratory models, such as the mouse. Wild sea lions, in contrast, experience many of these factors throughout daily life, including multiple layers of stressors like infectious agents, exposure to pollutants, nutrition, and environmental influences, all of which are arguably more representative of how cancer develops in the “real world.”
Cancer in sea lions was first discovered in 1979 where researchers found that between 18-23 percent of adult sea lions admitted to the Center’s hospital have died of the fatal disease. Now, after more than three decades of research, scientists have demonstrated that the cancer affecting up to one in four adult California sea lions that received a necropsy, or animal autopsy, at The Marine Mammal Center in Sausalito, CA, is caused by a sexually transmitted herpesvirus. The cancer, known as sea lion urogenital carcinoma, has clear parallels to cervical cancer in humans—which can be caused by the human papillomavirus (HPV)—and is currently thought to be a relevant model for studying cancer in humans.
The Marine Mammal Center’s chief pathologist Pádraig Duignan, right, and fellow Maggie Martinez perform a necropsy on a California sea lion that was euthanized due to untreatable cancer (Bill Hunnewell / Marine Mammal Center).
A second recently published paper led by the same team showed that pollutants such as Polychlorinated biphenyls (PCBs) and dichloro-diphenyl-trichloroethane (DDT) play a significant role in the development of this cancer. This is particularly relevant to Southern California where there is a large DDT dumpsite in the Southern California bight, where the majority of the sea lion population gather each year to give birth and raise their pups.
This research is important in many ways. It not only highlights the #Timescales that are often involved in basic research for the understanding of disease etiology but also emphasizes the cross-sectional nature of basic research; helping humans and the animals themselves—in this case sea lions. Dr. Alissa Deming, the lead author of the study states:
“The confirmation that this is a virally induced cancer combined with the knowledge that contaminants play a significant role in the cancer’s development means that we can use these sea lions as a naturally occurring disease model to better understand how cancer develops and spreads in all species, including humans.”
~Speaking of Research
*Taken from the press release from Marine Mammal Center and edited for style and content.
Speaking of Research 
Sea lions are on the verge of extinction and their breading area is affected by DDT pollution. And they are getting cancer. Tasmanian devil is another animal at the verge of extinction and their reproduction is affected due to lack of breast milk to feed the new born. They are also getting cancer. Humans have voluntarily reduced reproduction & getting many reproductive organs removed or made nonfunctional. Our cancer rate is also increasing .Can you see a link? **Comment edited to remove advertising, which is prohibited on our site; 4/8/21)**