A specific cancer of epithelial origin was first diagnosed in California sea lions at The Marine Mammal Center in 1979. Approximately 26% of adult stranded sea lions that die are diagnosed with cancer.
The Center collects samples from each of these patients to measure environmental exposure to carcinogens, or cancer-causing substances. Researchers at the Center also discovered that these sea lions are infected with a herpesvirus similar one that causes Kaposi's sarcoma in humans. Future research will determine the factors, such as pollutants or genetics that allow the virus to invade sea lion tissues and cause cancer.
Approximately 26 percent of adult stranded sea lions that die are diagnosed with cancer, which is a very high prevalence for a population of wild animals. 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.
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, The Marine Mammal Center worked with an array of researchers from the international scientific community to form the Sea Lion Cancer Consortium to highlight the scientific body of work currently underway in investigating cancer in sea lions.
Cancer Research at The Marine Mammal Center
Over the last 40 years, our veterinarians and scientists have contributed to a number of scientific papers on cancer in marine mammal populations, some of which can be viewed here:
Peñín, I., Levin, M., Acevedo-Whitehouse, K., Jasperse, L., Gebhard, Gulland, F.M.D.,and S. De Guise. 2018. Effects of polychlorinated biphenyls (PCB) on California sea lion (Zalophus californianus,) lymphocyte functions upon in vitro exposure. Environmental Research 167:708-717.
Deming, A.C., Colegrove, K.M., Duignan, P.J., Hall, A.J., Wellehan, F.X., Gulland, F.M.D. 2018. Prevalence of urogenital carcinoma in stranded California sea lions (Zalophus californianus) from 2005-2015. Journal of Wildlife Disease (Short Communications). 54(3).
Leathlobhair, M.N., Gulland, F.M.D., Murchison, E.P. 2017. No evidence for clonal transmission of urogenital carcinoma in California sea lions (Zalophus californianus). Research One 2017 2:46.
Cortes-Hinojosa, G., Gulland, F.M.D., DeLong, R., Gelatt, T., Archer, L., Wellehan Jr., J.F.X. 2016. A novel gammaherpesvirus in Northern fur seals (Callorhinus ursinus) is closely related to the California sea lion (Zalophus californianus) carcinoma-associated otarine herpesvirus-1. Journal of Wildlife Disease. 52(1): 88-95.
Browning, H.M., Gulland, F.M.D., Hammond, J. A., Colegrove, K.M., Hall, A. J. 2015. Common cancer in a wild animal: the California sea lion (Zalophus califonianus) as an emerging model for carcinogenesis. Philosophical Transactions Royal Society B. 370: 20140228.
Randhawa, N., Gulland, F., Ylitalo, G. M., DeLong, R., & Mazet, J. A. (2015). Sentinel California sea lions provide insight into legacy organochlorine exposure trends and their association with cancer and infectious disease. One Health, 1: 37-43.
Browning, H.M., Acevedo-Whitehouse K., Gulland, F.M.D., Hall, A.J., Finlayson, J, Dagleish, M.P., Billington, K.J., Colegrove, K, Hammond J.A. 2014. Evidence for a genetic basis of urogenital carcinoma in the wild California sea lion. Proc. R. Soc. B 281: 20140240.
The Marine Mammal Center’s Cancer Research in the News
Scientists Puzzled By High Cancer Rate Among West Coast Sea Lions – Oregon Public Broadcasting
Cancer at Sea – bioGraphic