Page 703 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

CHAPTER 32 Ocular Tumors 681

or metastasis. Such precise timing, however, is seldom attainable
in a clinical setting, and enucleation is commonly performed if
iridal pigment changes have been demonstrated to progressively
VetBooks.ir increase to the point that virtually the entire iridal surface is
involved, pigmented cells are present in the trabecular meshwork,
the pupil is distorted (indicating iridal invasion), ciliary body or
scleral invasion is threatened, uveitis is present, or glaucoma is
impending. Although it would seem logical that early enucleation
would optimize survival, this is unproved. In one study, enucle-
ation has been shown to markedly enhance the rate of metastasis
56
in cats with feline sarcoma virus–induced uveal melanomas. The
applicability of this experimental model to spontaneous disease,
however, is unclear and neither feline sarcoma virus nor FeLV were
found in a study of 10 eyes with spontaneous diffuse iris mela-
57
noma. Some ophthalmologists have attempted to ablate small,
focal, hyperpigmented foci on the iris of cats with a diode laser,
thereby preserving vision and the eye. The long-term success rate
and side effects of this procedure, however, are not known. Finally,
most slowly progressing lesions are simply monitored, ideally by
comparison to baseline photographs. This option is particularly • Fig. 32.7 Posttraumatic sarcoma in a cat. (Image courtesy Dr. Elizabeth
suitable for older cats with other diseases that limit their expected Adkins.)
lifespan. In many cats, progression may be so slow as to permit the
patient to be followed for many years to a decade or more without
apparent metastasis. Because of the risk of posttraumatic sarcoma, many clinicians
are cautious about cataract surgery, intravitreous injections of gen-
Prognosis tamicin for the treatment of glaucoma or the use of an intrascleral
The metastatic potential of feline uveal melanomas has been corre- prosthesis in cats. The cell of origin varies and is not definitively
lated with the extent of ocular involvement seen histologically. 50,54 known for all three subtypes. There is good evidence that the spin-
Because the tumor is relatively slow-growing, however, the period dle cell variant originates from the lens epithelial cell, and that the
until metastatic disease becomes apparent may be measured in initial pathogenesis of the tumor is related to lens capsule rupture,
years, and even then, substantial additional time may elapse before release, and proliferation of the lens epithelial cells and epithelial-
the metastasis is life threatening. Cats with tumors confined to to-mesenchymal transition, leading to the sarcoma phenotype
iris stroma and trabecular meshwork at the time of enucleation of the tumor. 63,64 Neoplastic cells of the round cell variant are
have survival times comparable to those of age-matched controls. positive on immunohistochemistry for CD79a (a B-lymphocyte
Enucleation after the tumor has invaded into the ciliary body but marker) and this variant likely represents a form of anaplastic,
65
not the sclera warrants a poorer prognosis, but the median survival primary ocular, B-cell lymphoma. Chronic inflammation may
50
time (MST) is still approximately 5 years. Enucleation after the support neoplastic transformation of a pluripotent cell. 58–60 These
tumor has invaded into the ciliary body and the sclera merits an tumors, often within the same eye, exhibit a spectrum of changes
50
even poorer prognosis, with an MST of approximately 1.5 years. ranging from granulation tissue to fibrosarcoma, osteosarcoma,
The MST is also reduced if secondary glaucoma has occurred. and anaplastic spindle cell sarcoma. 59,60 All of these tumors tend
50
In one study of 47 cats enucleated for diffuse iris melanoma, con- to circumferentially line the choroid and quickly infiltrate the ret-
54
firmed or suspected metastasis occurred in nine cases. However, ina and optic nerve. 59,60 The round cell variant tends to infiltrate
cats being enucleated for diffuse iris melanoma most likely reflect the retina early. 65,66 White or pinkish discoloration of the affected
the more extensive form of the disease and the rate of metastasis in eye or change in the shape or consistency of the globe are the most
cats with all forms of diffuse iris melanoma is likely substantially common presenting signs. Skull radiographs may demonstrate
lower. bone involvement or metallic foreign bodies. 61
Because this tumor is uncommon, many ophthalmologists will
Feline Ocular Posttraumatic Sarcoma not remove a comfortable phthisical feline eye unless it changes
appearance. The advanced stage at which many of these tumors
Sarcomas after ocular trauma, although uncommon, are second are first identified, however, and the propensity for early optic
only to melanomas in frequency as a primary ocular tumor of cats nerve involvement indicate that enucleation at this point may be
(Fig. 32.7). 58–61 In the COPLOW collection, 8% of feline ocular only palliative and not prolong life. This has led some authors to
tumors are posttraumatic sarcoma. These tumors are subdivided advocate prophylactic enucleation of phthisical feline eyes or of
into three morphologic subtypes: spindle cell sarcoma (the most feline eyes that are blind and have been severely traumatized or
common), round cell sarcoma (posttraumatic lymphoma), and are chronically inflamed. 58,61 Further support for this approach
osteosarcoma/chondrosarcoma. All three have similar histories comes from the observation that approximately 7.5% of globes
leading up to tumor presentation. Cats that are 7 to 15 years of removed prophylactically in the COPLOW collection already
age are most commonly affected, the latency period after trauma have tumors. Extension beyond the sclera or into the optic nerve
averages 5 years, and 67% of affected cats are males or neutered may occur and are poor prognostic indicators, further supporting
59
males. Damage to the lens and chronic uveitis may be risk fac- the concept of early enucleation. As much of the optic nerve as
tors. 58–60 Ciliary body ablation with gentamicin for glaucoma possible should be removed during enucleation for confirmed or
may also be a risk factor. 62 suspected ocular sarcoma so that the extent of infiltrative disease