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 testicle1. 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, Lipscomb TP. Malignant seminoma with metastasis and herpesvirus infection in a free-living sea otter (Enhydra lutris). J Zoo Wildl Med. 1998;29:35–39.
2. Stetzer E, Williams TD, Nightingale JW. Cholangiocellular adenocarcinoma, leiomyoma, and pheochromocytoma in a sea otter. J Am Vet Med Assoc. 1981;179:1283.
3. Thomas NJ, Creekmore LH, Pattison C. Causes of mortality in southern sea otters (Enhydra lutris nereis). In: Proceedings of the Wildlife Disease Association. 1994:52.
4. Williams TD, Pulley LT. Leiomyomas in two sea otters (Enhydra lutris). J Wildl Dis. 1981;17:401.