Page 1294 - Clinical Small Animal Internal Medicine

1232 Section 11 Oncologic Disease

Table 134.1 World Heath Organization clinical staging scheme It is important to note that the presence of an inflam­
VetBooks.ir Remarks matory process within enlarged lymph nodes may con­
for lymphoma in domestic animals
found a diagnosis since reactive lymphoid hyperplasia
can be difficult to distinguish from lymphoma. This
occurs commonly in the mandibular lymph nodes (due
Anatomic location to dental disease or ear infections), and evaluation of
A Generalized these nodes should be avoided if possible.
B Alimentary A definitive diagnosis of lymphoma may require
C Thymic further analysis to determine if a clonal population of
D Skin lymphocytes is present. This can be accomplished via
E Leukemia polymerase chain reaction‐based assay evaluating anti­
gen receptor rearrangements (PARR). The presence of a
F Other clonally expanded population of cells strongly supports a
Stage diagnosis of lymphoma as it is uncommon in a reactive
I Involvement of single lymph node or lymphoid process. It should be noted, however, that this test can
tissue in a single organ result in a high percentage (upwards to 25%) of false neg­
II Multiple involved lymph nodes in a single region atives. An alternative to PARR is a diagnostic test called
III Generalized lymph node involvement flow cytometry. This assay relies on monoclonal anti­
IV Involvement of the liver and/or spleen (+/‐ stage III) bodies and fluorescent markers to help confirm a diag­
V Presence of lymphoma in the blood/bone nosis of lymphoma by evaluating for aberrancies and
marrow and/or involvement of other organ systems determining the phenotype of leukocytes within a fresh
(+/‐ stage I–IV) sample of blood or tissue (e.g., lymph node, effusions).
Because flow cytometry requires living cells to complete
Substage
a No systemic signs of illness the assay, an abundance of dead or dying cells will
confound a definitive result.
b With systemic signs of illness Ideally, cytology should be used as a first‐line test fol­
lowed by confirmation with histology. A biopsy of lymph
node or other affected tissue can be obtained surgically
The most common presentation is that of an asymp­ or via needle core biopsy. An excisional biopsy is pre­
tomatic dog with nonpainful but markedly enlarged ferred, as it allows for a more thorough classification of
peripheral lymph nodes which would be classified as the type of lymphoma by preserving the architecture of
stage III, substage a (see Table 134.1). the affected tissue. Biopsy samples also provide adequate
In general, dogs with stage V lymphoma will present tissue to perform immunohistochemical phenotyping
with clinical signs related to the anatomic location of the for prognostic information by distinguishing between B
disease. For example, dogs with bone marrow infiltration and T cell forms.
may present with cytopenias, fever, sepsis or hemor­
rhage. Dogs with marked pulmonary involvement may Histologic Classification
present in respiratory distress. Lymphomas are a complex group of diseases that vary
As lymphoma has the potential to cause a wide array of clinically from indolent to aggressive, and from poorly
clinical syndromes, it should be considered as a potential controlled to manageable with treatment.
cause of any unexplained disorder in high‐risk breeds Indolent forms of lymphoma are uncommon and
until proven otherwise. poorly understood. These low‐grade forms of lymphoma
are relatively slow growing and are associated with long
survival times with limited or no therapy. Examples
Diagnosis/Clinical Staging include marginal zone lymphoma, follicular lymphoma,
A diagnosis of canine lymphoma can be achieved via fine B or T cell small cell lymphoma, and T zone lymphoma.
needle aspiration (FNA) and cytologic evaluation of The majority of dogs have a multicentric intermediate
an enlarged peripheral lymph node or tumor tissue. or high‐grade variety, with diffuse large lymphoblastic B
Cytology supportive of lymphoma will demonstrate a cell being the most common. While higher‐grade lym­
population of large or intermediate‐sized lymphocytes phomas tend to be more responsive to chemotherapy,
comprising the majority (>50%) of cells. Small cell lym­ the duration of tumor control is short when compared to
phoma is an exception, as it may not appear cytologically animals with low‐grade lymphoma, in which long sur­
malignant. vival is often achieved with minimal to no treatment.