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California sea lion with mouth open

Cancer - High Prevalence in California Sea Lions

Using three decades of data collection and analysis, the Center’s research revealed an extremely high prevalence of cancer in California sea lions.

A specific cancer of epithelial origin was first diagnosed in California sea lions at The Marine Mammal Center in 1979. Since then, researchers have determined that approximately 20 percent of adult stranded sea lions that die have cancer.

While there is more to be learned about the complex factors that play into the development of this disease, what we learn from these animals contributes to research that could eventually lead to cures for humans.

How Do Sea Lions Get Cancer?

Researchers at the Center discovered that these sea lions are infected with a herpesvirus similar to one that causes Kaposi's sarcoma in humans. In order to study this cancer, our researchers collect samples from each patient, fostering greater understanding of what might be causing the alarming cancer occurrence—including environmental and genetic factors.

Cancer development is a multi-step process during which damage to the genetic material of cells (DNA) arises from the interaction between a number of factors. These may include environmental factors such as chemical contaminants, infection by tumor-promoting viruses and the animals' own genetic predisposition to develop the disease.

People with Kaposi’s sarcoma generally have been smokers or exposed to toxins, so the latter may apply to marine mammals. High levels of persistent organic pollutants such as DDT and PCBs have been found in the blubber of California sea lions.

Using samples collected from hundreds of patients, the Center's researchers proved that a sexually transmitted herpesvirus causes the alarming cancer occurrence, and that pollutants such as PCBs and DDT play a significant role both as primary carcinogens (or cancer-causing substances) and as co-factors in the development of this cancer.

The research the Center conducts after the death of a sea lion with cancer is invaluable as this kind of work is not possible with human subjects. The Center's findings show that sea lion pups are exposed to PCBs while in utero, a factor that has important health effects later in their lives as PCBs can alter organ development.

In 2010, Center scientists brought together an array of international researchers to form the Sea Lion Cancer Consortium to further investigate this disease, and this work continues today.

Research Insights

Cancer Research at The Marine Mammal Center

Cancer was first diagnosed in California sea lions at The Marine Mammal Center in 1979. Since then, our veterinarians and scientists have contributed to a number of scientific papers on cancer in marine mammal populations.

Cancer in the News

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