Page 1298 - Clinical Small Animal Internal Medicine

1236 Section 11 Oncologic Disease

transplantation (bone marrow transplant), and immuno­ Signalment
VetBooks.ir therapy. These treatment strategies have variable success There is a bimodal distribution for feline lymphoma in
and continue to be an active area of investigation.
which retroviral‐positive cats present with lymphoma at
a young age (1–3 years) and virus‐negative cats present
at an older age (10–13 years). Currently, the median age
Feline Lymphoma at presentation is approximately 11 years. There is no sex
predilection and any breed of cat can be affected,
Etiology/Pathophysiology although Siamese cats are overrepresented, suggesting a
Lymphoma (LSA) is one of the most common neoplasms genetic susceptibility to the disease.
in the cat and can present in a variety of ways, depending
on the organ(s) affected. An association with retroviral History and Clinical Signs
infection has been firmly established, with approximately
25% of feline leukemia virus (FeLV)‐positive cats devel­ Location of the tumor appears to be the determinant
oping lymphoma during their lifetime. Feline immuno­ of clinical signs and prognosis in feline lymphoma.
deficiency virus (FIV) has also been implicated in the Consequently, the WHO staging system is not used.
development of lymphoma, although its true contribu­ Instead, lymphoma is generally divided into different
tion has been difficult to determine since it often occurs anatomic classifications: mediastinal, gastrointestinal,
in conjunction with FeLV. Chronic immunosuppression multicentric, and miscellaneous sites (such as nasal and
secondary to retroviral infection is thought to play a role renal).
in this association. This correlates with the increased
incidence of lymphoma in cats receiving chronic Mediastinal Lymphoma
immunosuppressive drugs after renal transplantation. Young cats typically present with a mediastinal form of
Collectively, these findings parallel an increased inci­ lymphoma with acute‐onset dyspnea, which rapidly
dence of lymphoproliferative cancers in humans with progresses as the tumor begins to occlude lymphatics,
human immunodeficiency virus (HIV) or those receiv­ leading to pleural effusion. Physical examination may
ing chronic immunosuppressive therapy. reveal a noncompressible cranial thorax and muffled or
The underlying cause of nonretroviral‐induced feline caudodorsal displacement of cardiac sounds.
lymphoma is not completely understood. It is likely
that chronic inflammation plays a role given that feline Alimentary Lymphoma
lymphomas frequently arise in organs or sites affected Alimentary lymphomas usually involve the stomach and
by chronic inflammation. For example, a correlation intestines of older cats. Gastrointestinal tumors may be
between chronic inflammatory bowel disease and ali­ discrete or diffuse. The primary clinical signs are anorexia
mentary lymphoma has been proposed. Comparatively, and weight loss, although some cats may also present
humans with celiac disease have a similar predisposition with vomiting and/or diarrhea. With these clinical signs,
towards lymphoproliferative disorders and cancer. it is important, though often difficult, to differentiate
Recent studies have also demonstrated that chronic lymphoma from inflammatory bowel disease.
exposure to environmental tobacco smoke is associated
with an elevated risk for gastrointestinal lymphoma Extranodal Lymphoma
in cats. Cats with other forms of lymphoma (e.g., nasal, renal,
CNS, laryngeal) will present with clinical signs reflecting
the anatomic location.
Epidemiology
Lymphoma is the most common neoplasm of the hemat­ Diagnosis
opoietic system of cats, with an estimated incidence of
200 per 100 000 cats. As described in dogs, a diagnosis of lymphoma can be
Studies have demonstrated that FeLV‐positive cats achieved via fine needle aspiration or surgical, endo­
have a 60‐fold or greater relative risk of the cancer. FIV scopic or needle biopsy of affected tissue. As noted
infection also increases the relative risk of lymphoma previously, a definitive diagnosis via a fine needle aspi­
5–6‐fold. rate can be confounded by an insufficient or nondiag­
While the incidence of feline lymphoma has not nostic sample, or if there is a significant component of
changed with the development of effective antiviral inflammation present. Because alimentary lymphoma is
vaccines, the most common presentation of lymphoma easily confused with inflammatory bowel disease (IBD),
is now in older retrovirus‐negative cats. a full‐thickness tissue biopsy is often necessary to