Lymphoma (LSA) is one of the most common feline malignancies, comprising approximately 30% of all reported tumors. While not
curable, LSA may respond quite well to therapy and can be a very satisfying neoplasm to treat.
The age of cats affected has increased over the past 10 years, due to the decline in FeLV+ cases. Middle-aged to older cats
are mainly affected. Young cats with LSA are often FeLV+.
FeLV is linked with most forms of LSA except the GI form. FeLV+ LSA is a T cell variant and occurs in younger cats (2 to 4
years). The risk of developing LSA is increased by 5x with FIV infection and by 77x with FeLV and FIV co-infection. FeLV can
directly cause malignant transformation, while FIV is thought to predispose to lymphoma via immune dysfunction. Inflammatory
bowel disease may ultimately progress to lymphoma, but this theory is not proven.
Presenting complaints in cats depends on the form of LSA affecting the patient. As the GI form is the most common, signs include
any or all of the following: weight loss, inappetance, lethargy, vomiting, and/or diarrhea. Multicentric cases will usually
be ill and have enlarged lymph nodes ("lumps" noted by owner). Mediastinal LSA causes dyspnea (from the mass or secondary
pleural effusion) and/or regurgitation (also a mass effect). Extranodal LSA also will present with concerns based on location:
sneezing/epistaxis for nasal, paresis/paralysis for CNS, systemic illness with the renal form, and blindness or discomfort
in ocular cases.
Depending on the form of the cancer, the diagnosis of LSA in cats may be achieved with fine needle aspirate (FNA) or may require
histopathology. Situations where biopsies are indicated include the GI form that is microscopic and diffuse, multicentric
lymphoma (peripheral lymph nodes can be enlarged for a number of non-neoplastic causes which may not be cytologically distinguishable),
nasal and cutaneous LSA.
As LSA is almost always a systemic disease, staging to determine extent of disease is important for prognosis and monitoring
response to therapy. Many of the specific forms of LSA do not stay isolated to the primary location. For example, renal LSA
may progress to involve the CNS, and spinal LSA frequently involves the bone marrow. However, staging may not be indicated
in cats that have a very poor prognosis at diagnosis (eg FeLV+ mediastinal LSA, leukemia).
Diagnostic evaluation of cats with LSA includes a complete blood count, serum chemistry profile, urinalysis, FeLV/FIV testing,
bone marrow aspirate, thoracic and abdominal radiographs and abdominal ultrasound. Clinical substage is based on symptoms:
substage a is asymptomatic, substage b correlates with an ill patient.
Unlike in dogs, there are not many prognostic factors in cats that help to predict which cats will respond to therapy. The
anatomic location of the lymphoma may be prognostic; some forms may respond better than others. Such information is somewhat
unclear due to most studies grouping together cats with various forms in the remission/survival analysis, and due to small
numbers of cats in the studies. Other prognostic factors include clinical substage (b does worse) and FeLV status (+ have
decreased remission times). One of the most prognostic findings, which unfortunately cannot be assessed prior to treatment,
is response to therapy (cats that go into remission have greatly prolonged survivals).