Page 746 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

724 PART IV Specific Malignancies in the Small Animal Patient

syndrome and precaval syndrome may be observed. Pleural effu-
sion is observed in 50% of cases and characterized by serohem-
orrhagic to chylous effusion and, in most cases, neoplastic cells
VetBooks.ir (lymphoblasts) are identified. 546,548,550 Diagnostic suspicion may
begin with a noncompressible cranial thorax on physical examina-
tion and confirmation of a mediastinal mass/pleural effusion on
thoracic radiographs. Fine-needle aspirate (FNA) cytology of the
mass or cytologic evaluation of pleural fluid may be sufficient to
establish a diagnosis. In most cats, the finding of a monotonous
population of intermediate or large lymphoid cells will establish
a diagnosis; however, definitive diagnosis of lymphoma in cats
with a mediastinal mass and concurrent chylothorax can be chal-
lenging. CT appearance may be helpful, but generally does not
contribute to a definitive diagnosis. If large lymphocytes are not
identified in the pleural chylous effusion, then cholesterol and tri-
glyceride concentrations can be measured. 551 In chylous effusions,
the pleural fluid triglyceride concentration will be greater than
• Fig. 33.15 Fine-needle aspirate cytology of a lymph node in a cat with in the serum; however, anorectic cats may have lower triglycer-
Hodgkin’s-like lymphoma. The large lymphocytes have prominent nucleoli ide levels in the pleural fluid. A major differential for mediastinal
and smooth basophilic cytoplasm. Several binucleate lymphocytes are lymphoma is thymoma. The cytologic features of thymoma can be
present.
distinct from lymphoma in many cases, but the diagnosis can be
challenging because of a preponderance of small lymphocytes in
best treated with CHOP- or COP-based protocols (discussed thymoma. Mast cells can also be seen in up to 50% of aspirations
under I/HGAL earlier) and carry a less favorable prognosis, from thymomas. The addition of immunophenotypic and clonal-
whereas the former generally respond to less aggressive chlo- ity assessment may be helpful in equivocal cases.
rambucil/corticosteroid protocols and enjoy durable responses. In the largest report, cats with mediastinal lymphoma treated
Less is known regarding the treatment of Hodgkin’s-like lym- with either COP- or CHOP-based protocols experienced an over-
phoma involving solitary or regional nodes of the head and all response rate of 95% with a MST of 373 days (980 days if CR
neck. 541,542 Clinical outcome after surgical extirpation of or was achieved). 548 In contrast, mediastinal lymphoma in young
RT to the affected node (or nodes if a reasonable number) is FeLV-positive cats is generally associated with a poor prognosis
often associated with long-term disease control and MSTs of and MSTs of approximately 2 to 3 months are expected after treat-
approximately 1 year, suggesting that it is a more indolent form ment with CHOP- or COP-based protocols. 428,524
of lymphoma. Eventual recurrence in distal nodes after surgical
excision or RT is common, and the author currently offers cli- Extranodal Lymphoma
ents the option of adjuvant chlorambucil/corticosteroids after
surgery. This theoretically may have benefit; however, insuf- Collectively, extranodal lymphoma represents the second most
ficient data currently exist to document a survival advantage common site of lymphoma after GI lymphoma in cats. 431 The
with this approach. most common extranodal sites for lymphoma in cats include nasal
(including nasopharyngeal and sinonasal), kidney, CNS, laryngeal
Mediastinal Lymphoma and tracheal, cutaneous, subcutaneous, and ocular.
The clinical signs associated with feline extranodal lymphoma
The mediastinal form can involve the thymus and mediastinal and are variable and depend on anatomic location and extent of dis-
sternal lymph nodes. Pleural effusion is common. In two large com- ease. Many, if confined to the primary site (stage I), will appear
pilations, 63% of cats with thymic disease and 17% of cats with clinically healthy. However, cats with lymphoma, regardless of
pleural effusion were documented as having lymphoma. 546,547 site, may present with nonspecific constitutional signs including
Hypercalcemia occurs frequently with mediastinal lymphoma in anorexia, weight loss, lethargy, or depression. Secondary bone
dogs, but is rare in cats. The majority of cats with mediastinal lym- marrow infiltration, although uncommon, may lead to anemia.
phoma in older reports were young (median age, 2–4 years), FeLV Signs related to paraneoplastic hypercalcemia (polyuria/polydip-
positive, and had T-cell immunophenotype tumor; however, many sia [PU/PD]) can occur in cats, however, much less commonly
reports did not report immunophenotypic data. 427,428,433–435,548 than in the dog. In one survey of hypercalcemia in cats, approxi-
The disease is confined to the mediastinum in most cases. A form of mately 10% were diagnosed with lymphoma of various anatomic
mediastinal lymphoma also occurs primarily in young, FeLV-nega- types. 552
tive Siamese cats that appears to be less biologically aggressive and For most cats with suspected extranodal lymphoma, the diag-
more responsive to chemotherapy than FeLV-associated forms. 533 nostic evaluation should include a baseline assessment consist-
In a more recent report of 55 cats with mediastinal lymphoma from ing of a CBC with differential cell count, platelet count, serum
the United Kingdom, the majority were antigenically FeLV/FIV chemistry profile, urinalysis, and retroviral (FeLV/FIV) screen.
negative, young (median age, 3 years), male (3.2:1 male-to-female Serum biochemistry profiles can help establish the overall health
ratio), and nearly one-third were Siamese. 548 In this large cohort, of the animal, as well as, in some cases, suggest site-specific tumor
immunophenotype was not reported. involvement. For example, increased liver enzymes levels may
The clinical signs associated with mediastinal lymphoma indicate hepatic infiltration and increased BUN and creatinine
include dyspnea (80%), tachypnea, and a noncompressible cra- may indicate renal lymphoma. Hypoglycemia was reported in
nial thorax with dull heart and lung sounds. 549 Rarely, a Horner’s approximately one-third of cats with lymphoma in one Australian