At a recheck examination three months after surgery, the cat was doing well, but the enlarged area was still present in the
right orbit. The right submandibular lymph node was not enlarged. A repeat ultrasonographic examination of the orbit demonstrated
that the mass had not changed in size or shape since the last examination. Thus, the owner elected to continue to monitor
the cat's health rather than pursue radiation therapy.
A year and a half after the exenteration, the cat continues to do well. The cause of the lymphoma remains unknown. It is also
unknown whether the previous blindness of unknown pathogenesis in the eye and the onset of the neoplasm are associated.
Lymphomas, the most common tumors in domestic cats,2 are solid tumors composed of neoplastic cells of lymphocytic lineage.1 Lymphoma is often more difficult to diagnose in cats than in dogs because in dogs, multicentric distribution and generalized
lymphadenopathy are common, while lymphoma in cats usually involves internal structures such as the alimentary tract,3-5 thymus,3 and mediastinum.6 Solitary lymph node involvement has been reported in cats as well, and most commonly involves lymph nodes of the head and
face.5 In cats, ocular lymphomas have been reported in the anterior uvea,5 orbit,7 and conjunctiva.8,9
Conjunctival lymphomas are relatively rare, extranodal neoplasms that have been reported in people,10 horses,11 and cats.8,9 They probably arise from the mucosa-associated lymphoid tissue present in the conjunctiva, which would be consistent with
the B-cell immunophenotype of this cat's lymphoma. Conjunctival lymphoma has the best prognosis of any ocular adnexal lymphomas.
In a retrospective study, only 36 of 117 (31%) patients with conjunctival lymphoid infiltration already had or eventually
developed systemic lymphoma.10 The study suggested that the tumor's location when the disease was first identified was prognostic for the development of
systemic lymphoma and that patients with tumors initially arising from extra-limbal sites (e.g. fornix or midbulbar) were less likely to develop systemic lymphoma.10 However, too few reported cases of this tumor exist to determine whether tumor location is a prognostic indicator in cats.
Immunocompromised pets and people
In people, conjunctival lymphoma occurs with increased frequency in immunodeficient individuals and may be associated with
viral infections or may be familial.1 Lymphoma in cats is often associated with viremia or latent FeLV infection12; however, as testing for FeLV infection and vaccinations have increased, the incidence of FeLV-positive lymphoma has decreased.13 In the alimentary and mediastinal forms of feline lymphoma, FeLV infection worsens the prognosis for long-term survival
and response to chemotherapy.14 However, the association between FeLV infection and conjunctival lymphoma in cats is unknown. In both of the reported cases
of conjunctival lymphoma and in the cat presented here, the FeLV test results were negative. Two of the three cats survived
long-term (> 1 year),9 while the remaining one was lost to follow-up.8 FIV infection increases the incidence of lymphoma but is thought to play an indirect role in its tumorigenesis.13
Immunophenotyping is being performed in cases of lymphoma in many species to provide prognostic information,6,15 and these tumors have been classified according to cytochemical and immunologic markers.14 Immunophenotyping is more readily available for lymphoid tumors in dogs than in cats, and it is generally considered to
be less useful as a prognostic indicator in cats.6,16 Lymphoid tumors arise from T and B lymphocytes17 and from natural killer cells.14,17 As in this case, feline lymphoma is most often the B-cell type.15,18