Leukemia is the presence of cancer cells in the bone marrow itself. This is
different from lymphoma, the other common white blood cell cancer, because
lymphoma arises from tissues outside the bone marrow, such as lymph nodes
or the spleen. There are two forms of leukemia, acute and chronic. The
acute form usually has poorly differentiated stem cells, produces anemia,
drops in white blood cell count and a lot of secondary problems associated
with anemia and a severely deficient immune system. When bone marrow is
examined, acute leukemia usually causes the bone marrow to have a large
number of cancer cells, making up at least 30% of the bone marrow cells.
The chronic form of leukemia is different in that it is usually possible to
identify the type of cell that is proliferating, such as granulocytic
(neutrophil) leukemia, lymphobastic leukemia, eosinophilic leukemia or
lymphoid leukemia. White blood cell counts are usually elevated and
sometimes are extraordinarily high, such as 100,000 to 300,000
wbcs/ul. Clinical signs tend to be non-specific for this disorder, too but
enlarged lymph nodes and spleen, weakness, lethargy, lameness, fevers,
increased drinking and urinating, bleeding disorders, liver enlargement and
pale gums have been reported to occur.
The prognoses for acute lymphoblastic leukemia and for acute nonlymphoid
leukemia are both very grave, with most affected pets living only a short
time after it is possible to make a diagnosis of these conditions, even
with treatment. There is no consistently successful treatment plan that I
know of but l-asparaginase (Elspar Rx) was supposed to be helpful in some cases. This medication is not currently available, as far as I know, though.
Chronic lymphocytic leukemia and chronic nonlymphoid leukemias have a better prognosis, although there isn't sure treatment for them, either.