Page 1348 - Small Animal Internal Medicine, 6th Edition

1320 PART XII Oncology

Originally, it was reported that approximately 90% of cats confirmed acute leukemias should be evaluated for circulat-
with lymphoid and myeloid leukemias tested positive for ing FeLV p27 and for serum antibodies against FIV.
VetBooks.ir FeLV p27 with enzyme-linked immunosorbent assay or vival times than cats with AML. Survival times in cats with
With treatment, cats with ALL apparently have better sur-
immunofluorescence. As discussed in Chapter 78, because
the prevalence of FeLV infection is decreasing, most cats
months.
with leukemia diagnosed in the authors’ clinics have not ALL treated with multichemotherapy range from 1 to 7
been viremic for FeLV (i.e., they are FeLV negative). There have been several published reports of cats with
myeloid leukemias treated with single-agent or combination
Clinical Features chemotherapy. The treatment protocols have included single-
The clinical features and physical examination findings in agent cyclophosphamide or cytosine arabinoside, as well as
cats with acute leukemias are similar to those in dogs and combinations of cyclophosphamide, cytosine arabinoside,
are summarized in Table 80.3. Shifting limb lameness and and prednisone; cytosine arabinoside and prednisone; cyclo-
ocular or neurologic signs do not appear to be as common phosphamide, vinblastine, cytosine arabinoside, and predni-
in cats as in dogs with myeloid leukemias. sone; and doxorubicin, cyclophosphamide, and prednisone.
Survival times in these cats have usually ranged from 2 to 10
Hematologic Features weeks, with a median of approximately 3 weeks. Therefore,
More than three fourths of cats with AML and ALL have as in dogs, intensive chemotherapy does not appear to be
cytopenias; leukoerythroblastic reactions are common in beneficial in cats with acute leukemias.
2
cats with AML but extremely rare in those with ALL. In Low-dose cytosine arabinoside (LDA; 10 mg/m subcuta-
contrast to dogs, circulating blasts appear to be more neously q12h) has been used as an inductor of differentiation
common in cats with AML than in those with ALL. of the neoplastic clone. In several studies this treatment was
Sequential studies of cats with myeloid leukemias have observed to induce complete or partial remission in 35% to
revealed that the cytomorphologic features can change from 70% of humans with MDS and MPD. Moreover, although
one cell type to another over time (e.g., sequential diagnoses myelosuppression was observed in some patients, the treat-
of erythremic myelosis, erythroleukemia, and acute myelo- ment was exceedingly well tolerated and associated with
blastic leukemia are common in a given cat). This is one of minimal toxicity.
the reasons that most clinical pathologists prefer the term One of the authors (GC) treated several cats with MPD
myeloproliferative disorder (MPD) to refer to this leukemia using LDA and has observed in most complete or partial
in cats. remissions, with transient hematologic improvement.
Although no major toxicities were seen, the remissions were
Diagnosis and Treatment short-lived (3-8 weeks).
The diagnostic evaluation of cats with suspected acute leu-
kemia follows the same general sequence as that for dogs. If CHRONIC LEUKEMIAS
the changes in the CBC are not diagnostic, a bone marrow Chronic leukemias are becoming more common in cats; this
aspirate can provide information that may confirm the diag- may be due to the relative decrease in the prevalence of acute
nosis (Fig. 80.7). In addition, cats with suspected or leukemias, or it may represent a true phenomenon. CLL is
occasionally found incidentally during routine physical
examination. More often, cats with CLL are seen by a veteri-
narian because of a protracted history of vague signs of
illness, including anorexia, lethargy, and gastrointestinal
tract signs.
One author’s clinic (GC) previously evaluated seven
FeLV-FIV–negative cats with CLL that presented primarily
for anorexia and weight loss. Splenomegaly, hepatomegaly,
and/or lymphadenopathy were present on physical examina-
tion in all cats. On initial evaluation, the average hematocrit
was 26%, platelets averaged 258,000 cells/µL, and the total
white cell count was 63,000 cells/µL. The mean lympho-
cyte count was 48,200 cells/µL (range, 10,000-104,000/µL)
and were primarily small, well differentiated, with clumped
chromatin and often a cleaved or irregular nuclear mem-
brane (Fig. 80.8). Six of the seven cats had CD5+CD4+CD8−
FIG 80.7 (T-helper cell) immunophenotype (see Fig. 80.1). Six of the
Bone marrow aspirate from a cat with peripheral blood
cytopenias and absence of circulating blasts. Note the seven cats (86%) responded to treatment with chlorambucil
2
predominance of large immature myeloid cells, (20 mg/m , PO, q2 weeks) and dexamethasone (4 mg, PO,
characterized by round to kidney-shaped nuclei. A mitotic q1 week) or prednisolone (1 mg/kg, PO, q24 hours). MST
figure is evident (×1000). was 14 months (range, 1-34 months). A recent report of