Feline Ocular Sarcoma

Feline ocular sarcomas are malignant intraocular neoplasms that are often associated with a history of ocular trauma.  Cats appear to be the only species predisposed to the development of this neoplasia and the mean age is 12 years.  Affected cats often have a history of penetrating ocular injury resulting in the perforation of the lens, but trauma is not necessary.  The duration of ocular disease prior to the detection of the neoplasm ranges from several months to years.

  Although this neoplasia appears to be rare, any cat with a history of ocular trauma or chronic ocular disease should be evaluated if there are any changes in the eye.  Abnormalities include white discoloration (opacity), bulging and firmness of the diseased eye.  Sometimes cats show blindness and neurological signs resulting from neoplastic infiltration of the optic chiasm and brain via the optic nerve.

  Feline ocular sarcomas are locally invasive and have metastatic potential.  Tumors occupy the posterior iris and expand diffusely into the ciliary body, posterior chamber, retina and choroid.  Extraorbital invasion is common and may begin at the limbus or occur through the optic nerve.  The lens is invariably destroyed and significant inflammation accompanies tumor growth.  Whether this occurs because of the initial traumatic event or is secondary to ocular neoplasia is unclear.  The specific histologic diagnosis of tumor types is variable.  While fibrosarcoma is the most common diagnosis, osteosarcoma or undifferentiated sarcoma may occur.  There does not appear to be any variation in biologic behavior for different histopathologic types.  While the cell of origin has previously been unknown, Zeiss CJ et al reported recently that some of these tumors are of lens epithelial origin while others are of myofibroblastic origin.  Lens epithelial transformation appears to be limited to cats as these tumors have not been identified in dogs and humans.  Also, according to this study, feline ocular sarcomas demonstrate morphologic similarities to feline vaccine-associated sarcomas.  The suggested links between the two diseases include trauma, chronic inflammation with cell proliferation, and neoplastic transformation.

  Ocular ultrasonography may allow evaluation of the globe prior to surgery, although CT and MRI are more accurate imaging modalities.  Aspiration cytology and biopsy of regional (submandibular and retropharyngeal) lymph nodes should be performed if they are enlarged.  Metastases to regional lymph nodes have been seen in some cats.  Thoracic radiography should be obtained as pulmonary metastases have also been described.

  Enucleation is the treatment of choice for feline ocular sarcoma.  However, these are very invasive tumors; surgery may be ineffective in cats with extensive local spread.  Imaging is important to identify good surgical candidates.  When performing enucleating surgery, care must be taken to avoid placing strong traction on the optic nerve.  Several anecdotal accounts suggest that animals can become blind due to optic nerve dysfunction in the remaining eye following a routine enucleation.  A working hypothesis for this unfortunate outcome is mechanical damage to the contralateral optic nerve at the level of optic chiasm due to surgical traction.

  After surgery, metastasis or extension involving the central nervous system can be seen.  Radiation therapy may have a role in advanced, invasive ocular sarcomas, although the high dosages that are necessary require sophisticated computer planning equipment to minimize damage to the CNS.  Chemotherapy has not proven effective in the treatment of soft tissue sarcoma to date.  Doxorubicin and carboplatin could be offered for palliation.  However, euthanasia is often elected for affected cats due to the neurologic signs and poor prognosis.

-by Kyunga An, ECFVG Student
-edited by Dr. Pam Mouser, ADDL Graduate Student

References:

1. Dubielzig RR, Everitt J, Shadduck JA, Albert DM: 1990.  Clinical and morphologic features of post-traumatic ocular sarcomas in cats.  Vet Pathol 27: 62-65.

2. Dubielzig RR et al: 1994.  Morphologic features of feline ocular sarcomas in 10 cats: Light microscopy, ultrastructure and immunohistochemistry.  Prog Vet Comp Ophthal 4:7-12.

3. Ogilvie GK and Moore AS: 2001.  Feline oncology.  Veterinary Learning Systems. 266-267.

4. Peiffer RL and Simons KB: 2002.  Ocular tumors in animals and humans.  Iowa State Press. 291-292.