Reports of neoplasms in the sea otter (Enhydra lutris) have been sparse, considering the
attention this species has received due to the classification of the Southern sea otter as threatened and because of the
large numbers of carcasses examined following the Exxon Valdez oil spill. Neoplasms that have been reported include
leiomyomas,4 a leiomyoma concurrent with a cholangiocellular adenocarcinoma and pheochromocytoma,2
and a malignant seminoma in a retained testicle.1 In the southern sea otter, a carcinoma of probable
parathyroid origin, a lymphoproliferative disorder, and an osteosarcoma were thought to contribute to death while an
oligodendroglioma, leiomyoma, and a seminoma were considered incidental lesions.3 We report three sarcomas in
three sea otters submitted to the U.S. Fish and Wildlife Service in Anchorage, Alaska by the Alaska Sea Otter Commission
(a consortium of Native American subsistence hunters) through a statewide sea otter biosampling program. One tumor was a
7.7-kg chondrosarcoma attached to the last rib, another a 0.45-kg tumor on a hindlimb, and the last a 6.1-kg tumor
attached to the last rib. The gross and histologic features of the second and third tumors were most suggestive of a
peripheral nerve sheath tumor, however on immunohistochemistry, there was multifocal, faint staining with smooth muscle
actin and questionable multifocal staining with S-100. Differential diagnosis for these two tumors include a low-grade
fibrosarcoma with myofibroblastic differentiation and a peripheral nerve sheath tumor. Electron microscopy (EM) for viral
particles were negative on the chondrosarcoma and EM was not attempted on the other two tumors. Two of the tumors were
extremely large, resulting in compression of the pleural cavity, yet the animals were still able to forage for food.
1. Reimer DC, TP Lipscomb. 1998. Malignant seminoma with metastasis and herpesvirus
infection in a free-living sea otter (Enhydra lutris). J. Zoo Wildl. Med. 29:35-39.
2. Stetzer E, TD Williams, JW Nightingale. 1981. Cholangiocellular adenocarcinoma,
leiomyoma, and pheochromocytoma in a sea otter. J. Am. Vet. Med. Assoc. 179:1283.
3. Thomas NJ, LH Creekmore, C Pattison. 1994. Causes of mortality in southern sea otters
(Enhydra lutris nereis). Proc. Wildl. Dis. Assoc. Pp. 52.
4. Williams TD, LT Pulley. 1981. Leiomyomas in two sea otters (Enhydra lutris). J.
Wildl. Dis. 17:401.