Page 1344 - Small Animal Internal Medicine, 6th Edition

1316 PART XII Oncology

Treatment
BOX 80.1
The treatment of dogs with acute leukemias is usually unre-
VetBooks.ir Acute Lymphoblastic Leukemia or Lymphoma With warding. Most dogs with these diseases respond poorly to
therapy, and prolonged remissions are rare. Treatment failure
Circulating Blasts (Lymphosarcoma Cell Leukemia):
usually stems from one or more of the following factors:
Guidelines for a Clinical Diagnosis
1. If the lymphadenopathy is massive, the dog more 1. Failure to induce remission (more common in AML than
likely has lymphoma (see Fig. 80.2). in ALL)
2. If the dog is systemically ill, it is more likely ALL. 2. Failure to maintain remission
3. If bicytopenia or pancytopenia is present, ALL is the
more likely diagnosis. 3. The presence or development of organ failure resulting
4. If the percentage of lymphoblasts in the bone marrow from leukemic cell infiltration; this precludes the use of
is more than 40% to 50%, the dog is more likely to aggressive combination chemotherapy (i.e., because of
have ALL. enhanced toxicity)
5. If the cells are CD34 negative, it is more likely 4. The development of fatal sepsis, bleeding, or both caused
lymphoma. by already existing or treatment-induced cytopenias
6. If hypercalcemia is present, the more likely diagnosis
is lymphoma. Prolonged remissions in dogs with AML treated with
chemotherapy are extremely rare. In most dogs with AML,
ALL, Acute lymphoblastic leukemia. remissions in response to any of the protocols listed in Box
80.3 are uncommon. If patients do respond, the remis-
sion is usually extremely short-lived and survival rarely
BOX 80.2 exceeds 3 months. In addition, more than half of the dogs
die during induction as a result of sepsis or bleeding. In
Basic Diagnostic Principles for Dogs With recent studies, the survival times in dogs with acute leuke-
Suspected Leukemia mias were 8 to 55 days (Bennett et al., 2016; Novacco et al.,
1. If cytopenias or abnormal cells are present in 2015a).
peripheral blood, a bone marrow aspirate or biopsy Furthermore, the supportive treatment required in these
specimen should be obtained. patients (e.g., blood component therapy, intensive care mon-
2. If the spleen or liver is enlarged, a fine-needle itoring) is financially unacceptable to most owners, and the
aspirate of the affected organs should be obtained for emotional strain placed on the owner is also quite high. In
cytologic evaluation. humans, it costs more than $1 million to treat a child with
3. If blasts are present, blood and bone marrow leukemia. Therefore owners should be aware of all these
specimens should be submitted to a veterinary referral factors before deciding to treat their dogs.
laboratory for cytochemical staining or The prognosis may be slightly better in dogs with ALL;
immunophenotyping.
4. Other diagnostic tests (e.g., serologic tests or however, responses to treatment and survival times in these
polymerase chain reaction [PCR] testing for Ehrlichia patients are considerably lower than those in dogs with lym-
canis) should be performed if appropriate. phoma. The remission rates in dogs with ALL are approxi-
mately 20% to 40%, in contrast to those in dogs with
lymphomas, which approach 90%. Survival times with che-
motherapy in dogs with ALL are also shorter (average, 1-3
In addition to lymphoma, differential diagnoses in dogs months) than those in dogs with lymphoma (average, 12-18
with acute or chronic leukemias include other disorders of months). Untreated dogs usually live less than 2 weeks. Che-
the mononuclear-phagocytic or hematopoietic systems, such motherapy protocols used in dogs with acute leukemia are
as malignant or systemic histiocytosis; systemic mast cell listed in Box 80.3.
disease (mast cell leukemia); and infectious diseases such
as histoplasmosis, ehrlichiosis, anaplasmosis, bartonellosis,
leishmaniasis, mycoplasmosis, and mycobacteriosis. Box CHRONIC LEUKEMIAS
80.2 lists the basic principles of diagnosis that apply to all
dogs with suspected leukemia. Prevalence
The diagnosis of acute leukemia can be extremely straight- In dogs, CLL is far more common than CML; in addition,
forward (i.e., a dog that is evaluated because of weight loss, the latter is poorly characterized. One author’s hospital eval-
lethargy, hepatosplenomegaly, pallor, and central nervous uates approximately six to eight dogs with CLL a year,
system [CNS] signs and that has a WBC of >500,000/µL, whereas approximately one dog with CML is evaluated every
most of which are blasts, is most likely to have ALL), or it 3 to 5 years. CLL is one of the leukemias most commonly
may represent a challenge (i.e., a dog with unexplained cyto- diagnosed at diagnostic referral laboratories. Small-breed
penias of prolonged duration in which aleukemic AML-M 1 dogs are more likely to develop B-cell CLL than large-breed
subsequently develops). dogs (Bromberek et al., 2016).