A specific cancer of epithelial origin was first diagnosed in
California sea lions at The Center in 1979. The animals affected
are adult and subadult California sea lions of both sexes. Eighteen
percent of the sea lions in those age classes that die at The
Center have this type of cancer. This 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 this type
of cancer generally have been smokers or exposed to toxins.
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 cancer probably originates somewhere in the urogential
tract and is often first seen as a tumor in the sublumbar
lymph nodes. However, this cancer is highly invasive and metastatic
and can affect a large number of organs. Clinical signs of
this disease include swelling of perineum and vulva; swelling
of hind flippers; loss of feeling in hind end; anorexia; or
emaciation. There is no treatment for these animals, and the
condition is probably painful. The use of laparoscopy and
ultrasound, performed under anesthesia, to diagnose cancer
has allowed us to minimize suffering by allowing early diagnosis.
Animals with the disease are usually euthanized so that they
do not suffer.
We are a collaborating partner with U.C. at Davis and the
National Marine Fisheries Service on a $1.3 million three-year
grant awarded in 2000 by the National Institute of Health
to research the
factors involved in the high prevalence of cancer in California
sea lions.
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Cancer