For the Health of It
Equine Lymphosarcoma
Reprinted with permission from the January 2016 edition of Equine Disease Quarterly.
Lymphocytes are an important
component of the equine immune system. Like all cells within
the body, lymphocytes have the
potential to undergo neoplastic
(cancerous) transformation that
results in uncontrolled regulation
and growth. Lymphosarcoma is the
proliferation of neoplastic lymphocytes.
Equine lymphosarcoma is relatively common, but the exact
incidence is unknown. The majority of cases occur in horses aged
4-15 years, but cases have been
described in horses of all ages.
Epidemiologic studies suggest no
apparent gender or breed predisposition. Like many equine cancers,
the cause of lymphosarcoma is rarely identified, but certain bacteria
and viruses have been implicated in
its development.
Four anatomical categories are
frequently utilized for classification
of lymphosarcoma. These categories
include: multicentric (generalized
or within multiple locations), thymic (mediastinal, within the chest
cavity), alimentary (intestinal), or
cutaneous (skin or extranodal).
Clinical signs may develop
abruptly or over several months.
Signs can develop due to organ
dysfunction directly related to infiltration by neoplastic lymphocytes;
physical obstruction caused by neoplastic masses; or from neoplastic
byproducts (paraneoplastic syndrome). Depression, weight loss,
subcutaneous edema, fever, anemia,
and lymphadenopathy (swollen
lymph nodes) are the most com20 • Walking On
monly observed clinical signs, but
signs can vary based on the affected
organs. Multicentric, thymic, and
cutaneous forms can compress the
airways and esophagus and result
in respiratory or swallowing abnormalities. The intestinal form can
result in colic, diarrhea, and weight
loss. Cutaneous nodules may be
observed in or under the skin;
these masses can be influenced by
horm