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Saint Lawrence belugas

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One adult animal out of 5 suffered from cancer. (Cancer was observed in 27 % of examined adult animals from 1983 to 1998). In the western world, cancer causes 23 % of all deaths in humans, a percentage similar to that found in Saint Lawrence beluga. Such a high percentage had never been observed in any wild animal species, terrestrial or aquatic (with the important exception of fish). To our knowledge, this is the first population of wild mammals that can be compared to humans in this regard.

The rate of cancer in Saint Lawrence beluga is also much higher than that observed in other cetaceans. Only 28 other cases of cancer have been reported in wild and captive cetaceans worldwide. Thus, cancers reported in Saint Lawrence beluga represent about half of all cancers reported in cetaceans worldwide.

In addition, some of the cancers affecting Saint Lawrence beluga, such as cancer of the small intestines, are rare in all mammals, including humans. Yet, we have observed seven of these cancers in a population of 650 animals since 1983.
The examination of carcasses on the shore is rarely satisfactory. The rising tide can carry away samples. Snow and darkness can disrupt the examination as well. Since the beginning of the program, carcasses have generally been brought to the College of Veterinary Medicine. The 500-km transportation  is well worth the trouble because examinations are carried out under good conditions, in the necropsy room. This allows to determine the cause of death in one animal out of three. (Significant lesions are observed in almost every carcass examined). This high success rate is also due to the prompt report of stranded carcasses by the public, and to Mr. R. Plante and C. Guimont (FILMAR) who quickly recover and transport the carcasses. The icy waters of the Estuary also play an important role. Because water has a high thermal conductibility and a high specific heat, the carcass is rapidly cooled. Without this, the heat generated by fermentation would quickly accumulate and "cook" the carcass because of the thick layer of fat.
Cancer - anse intestinale Intestinal cancer in a beluga from the St Lawrence Estuary. Examined on May 23, 1993. The larger intestinal segment on the right is abnormally dilated because a malignant tumor (the irregularly sized masses in the center) distorted the intestinal architecture and obstructed the intestinal lumen. Food cannot pass and as a result, accumulates in the intestinal segment that is closest to the stomach (on the right).
Cancer - anse intestinale - vue microscopique Microscopic view of intestinal cancer in an adult beluga whale. The paler area delineated by the two arrows is a nest of tumor cells. Within this paler area, gland-like structures (white spaces) are lined by cancer cells. Cancer cells mimic the glands normally found in the intestinal mucosa. The "glands" are irregular and ill formed, in contrast with normal intestinal crypts. These glandular structures are not present where they normally should be, near the intestinal lumen. Rather, they are embedded deep in the muscular layers, where they destroy vital structures such as blood vessels.


Nature Reviews Cancer 9, 605 (August 2009) | doi:10.1038/nrc2698 Science and society : Wildlife cancer: a conservation perspective Denise McAloose & Alisa L. Newton

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