Page 1287 - Clinical Small Animal Internal Medicine

133 Lymphoid Leukemias, Myeloid Neoplasia, and Myelodysplastic Syndrome 1225

nonresponsive patients. Treatment of ALL requires
VetBooks.ir aggressive chemotherapy; CHOP‐based therapies like
those used in lymphoma are the most common proto­
cols. Remission rates of 25% have been reported but
remission times tend to be short.

Prognosis

Chronic lymphocytic leukemia is a slowly progressive
disease and many patients are monitored for months
before any therapy is instituted. Remission rates with
treatment are ~70–75% with overall survival times of >1
year. Immunophenotype has been shown to be predic­
tive with survival times for dogs with granular T‐CLL,
B‐CLL, and atypical CLL of 930, 480, and 22 days respec­
tively. Although the prognosis is good in the short term,
ultimately, CLL patients can experience an acute blast
crisis in which lymphoblasts replace mature lympho­
cytes (ALL) and response to aggressive treatment is poor.
Prognosis for dogs and cats with ALL is very poor.
Figure 133.2 Photomicrograph of lymphoblasts in the peripheral Median survival times of 3–128 days have been reported
blood of a dog with ALL. The cells are characterized by large size in ALL dogs with a CD34+ phenotype treated with
with prominent nucleoli. Wright Giemsa stain, 1000× CHOP‐based treatment protocols.
magnification. Source: Courtesy of Dr Jan Andrews, Antech Hematopoietic peripheral blood stem cell transplanta­
Diagnostics. tion (HSCT) is presently a viable treatment option
for dogs with leukemias. Although not widely available,
Other causes of a lymphocytosis (chronic ehrlichiosis, improved survival and cure are possible with this
Rocky Mountain spotted fever, and severe babesiosis in ad vanced form of therapy.
dogs; feline immunodeficiency virus [FIV], Toxoplasma
gondii, and chronic inflammatory bowel disease in cats)
should be ruled out if lymphocytic leukemia is not an Myeloid Neoplasia
obvious conclusion.
Myeloid neoplasms arise from clonally proliferating cells
in the bone marrow and manifest as either accumulation
Therapy
of neoplastic cells in the blood or lack of normal blood
Chronic lymphocytic leukemia can have a protracted cells. Myeloid neoplasms are divided into acute myeloid
clinical course and treatment is not usually instituted leukemia (AML) and myeloproliferative neoplasms
until specific criteria are met: the presence of periph­ (MPNs) which include chronic myelogenous leukemia
eral cytopenias (anemia, thrombocytopenia and/or (CML), polycythemia vera (PV), basophilic/eosinophilic
neutropenia), clinical signs associated with the disease, leukemia, and essential thrombocytosis. (Box 133.1).
peripheral lymphadenopathy, organomegaly, and/or a
peripheral lymphocytosis of >60 000 (although this is not Acute Myeloid Leukemia
standardized). The standard treatment for CLL is a com­
bination of the oral alkylating agent chlorambucil and Etiology/Pathophysiology
prednisone. The dose and frequency of chlorambucil can Acute myeloid leukemia is defined by an abnormal pro­
vary. In dogs it is typically given orally at 0.2 mg/kg or liferation of clonal cells in the bone marrow and periph­
2
6 mg/m orally once daily for 7–14 days, then reduced to eral blood that arise from a single immature blast cell.
2
0.1 mg/kg or 3 mg/m every other day thereafter. In cats, AML is divided into several subcategories based on
2 mg/cat every 48 hours is commonly used. Oral pred­ the Animal Leukemia Study Group’s 1991 proposal
nisone is used concurrently with chlorambucil at 1 mg/kg which was modeled after the human leukemia French‐
daily for 1–2 weeks, then 0.5 mg/kg every other day American‐British (FAB) Cooperative Group classifica­
thereafter. In cats, 10 mg/cat every 24 hours is commonly tions (see Box 133.1). In this system, myeloid leukemias
used. The addition of vincristine or the substitution of are divided into phenotypic subtypes based on morphol­
cyclophosphamide for chlorambucil has been used in ogy and cytochemistry profiling using an alphanumeric