Page 1347 - Small Animal Internal Medicine, 6th Edition

CHAPTER 80 Leukemias 1319

differentiate CML from leukemoid reactions (i.e., CML cells The survival times in dogs with CLL are quite long.
have the Philadelphia 1 chromosome, and the alkaline phos- Indeed, even without treatment, survival times of more than
VetBooks.ir phatase content of the neutrophils increases in the setting of 2 years are common. More than two thirds of the dogs with
CLL treated with chlorambucil (with or without prednisone)
leukemoid reactions and decreases in the setting of CML).
Chromosomal analysis of the cells in question may reveal
fact, most dogs with CLL do not die as a result of leukemia-
specific abnormalities that support a diagnosis of CML. As at the authors’ clinics have survived in excess of 2 years. In
a general rule, a final diagnosis of CML should be made only related causes but rather of other senior disorders.
after the clinical and hematologic findings have been care- In a study of 202 dogs with neoplastic lymphocytosis,
fully evaluated and the inflammatory and immune causes of which likely included both dogs with CLL and dogs with
neutrophilia have been ruled out. leukemic phase of lymphoma, expression of CD34 on flow
cytometry was associated with a negative prognosis (survival
Treatment times of 16 days). Dogs with B-cell proliferation (CD21 posi-
The clinician usually faces the dilemma of whether to treat tive) had shorter survival times than those with T-cell (CD8-
a dog with CLL. If the dog is symptomatic, has organo- positive) proliferations. Dogs with CD8-positive phenotype
megaly, or has concurrent hematologic abnormalities, treat- had longer survival times if the lymphocyte count was less
ment with an alkylator (with or without corticosteroids) is than 30,000/µL (1100 days versus 131 days); among the dogs
indicated. If there are no paraneoplastic syndromes (i.e., with B-cell phenotype, those with circulating small lympho-
immune hemolysis or thrombocytopenia, monoclonal gam- cytes had a significantly longer survival than those with large
mopathies), the authors use single-agent chlorambucil at a lymphoid cells (MST not reached versus 129 days) (Williams
dosage of 20 mg/m given orally (PO) once every 2 weeks et al., 2008).
2
(Box 80.4). If there are paraneoplastic syndromes, or the Recently, Comazzi et al. (2011) reported that dogs with
patient is symptomatic, the addition of corticosteroids (pred- T-CLL that received chemotherapy had approximately 3-fold
2
2
nisone, 50-75 mg/m PO q24h for 1 week, then 25 mg/m and 19-fold higher probability of surviving than dogs with
PO q48h) may be beneficial. B-CLL and atypical CLL, respectively. Old dogs with B-CLL
Because the growth fraction of neoplastic lymphocytes in survived significantly longer than did young dogs, and
CLL appears to be low, a delayed response to therapy is anemic dogs with T-CLL survived a significantly shorter
common. In a high proportion of dogs with CLL treated with time than dogs without anemia (Comazzi et al., 2011).
chlorambucil or chlorambucil and prednisone, it may take The treatment of dogs with CML using hydroxyurea (see
more than 1 month (and as long as 6 months) for the hema- Box 80.4) may result in prolonged remission, provided a
tologic and physical examination abnormalities to improve. blast crisis does not occur. However, the prognosis does not
This is in contrast to dogs with lymphoma and acute leuke- appear to be as good as that for dogs with CLL (i.e., survivals
mias, in which remission is usually induced in 2 to 7 days. of 4-15 months with treatment). The treatment of blast crises
is usually unrewarding. A novel therapeutic approach target-
ing tyrosine kinase in the neoplastic cells of humans with
BOX 80.4 CML using imatinib (Gleevec) has shown to be beneficial in
inducing remission; however, it is unknown if tyrosine
Chemotherapy Protocols for Dogs and Cats With kinase inhibitors are beneficial in dogs with this disease.
Chronic Leukemias

Chronic Lymphocytic Leukemia LEUKEMIAS IN CATS
2
Chlorambucil, 20 mg/m PO once every 2 weeks
2
Chlorambucil as above, plus prednisone, 50 mg/m PO ACUTE LEUKEMIAS
2
q24h for a week; then 20 mg/m PO q48h
COP Protocol Prevalence
2
Cyclophosphamide, 200-300 mg/m IV or PO once In the feline leukemia virus (FeLV)-free era, true leukemias
every 2 weeks are rare in the cat, constituting less than 15% of all hemato-
2
Vincristine, 0.5-0.75 mg/m IV once every 2 weeks poietic neoplasms. Although exact figures regarding the inci-
(alternating weeks with the cyclophosphamide) dences of leukemias and lymphomas are not available, these
Prednisone as in protocol 2; this treatment is continued neoplasms are extremely rare in the authors’ clinics.
for 6-8 weeks, at which time protocol 1 or 2 can be If cytochemical staining or immunophenotyping is used
used for maintenance to classify acute leukemias in cats, approximately two thirds
Chronic Myelogenous Leukemia are myeloid and one third are lymphoid. However, in con-
Hydroxyurea, 50 mg/kg PO q24h for 1-2 weeks; then trast to dogs, myelomonocytic leukemias (M 4 ) appear to be
q48h rare in cats.
Imatinib (Gleevec), 10 mg/kg PO q24h FeLV is commonly implicated as a cause of leukemias in
cats; however, the role of feline immunodeficiency virus
IV, Intravenous; PO, by mouth. (FIV) in the pathogenesis of these neoplasms is still unclear.