Page 1322 - Small Animal Internal Medicine, 6th Edition

1294 PART XII Oncology

CHAPTER 79
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Lymphoma

Lymphoma (i.e., malignant lymphoma, lymphosarcoma) is a (Modiano et al., 2005). For example, Boxers, Shih Tzus, and
lymphoid malignancy that originates from solid organs or Siberian Huskies have primarily T-cell tumors, whereas
tissues (e.g., lymph nodes, liver, spleen, eye); this distin- Cocker Spaniels and Basset Hounds have predominantly
guishes lymphomas from lymphoid leukemias, which origi- B-cell lymphoma; B- and T-cell tumors are almost equally
nate in the bone marrow (see Chapter 80). distributed in Golden Retrievers.
The age of cats with lymphoma at the time of presentation
Etiology and Epidemiology is bimodal, with the first peak occurring in cats that are
Early reports stated that approximately 70% of cats with lym- approximately 2 years of age and the second peak in cats that
phoma are persistently infected with feline leukemia virus are approximately 10 to 12 years of age. The cats that make
(FeLV) (Table 79.1). Although the prevalence of viremia in up the first peak are mainly FeLV positive, whereas those that
cats with lymphoma varies with the anatomic form of pre- make up the second peak are predominantly FeLV negative.
sentation (see later discussion), young cats with lymphoma As mentioned earlier, the prevalence of FeLV-positive cats
are generally FeLV positive, whereas older cats are FeLV neg- with lymphoma in the United States continues to decrease.
ative. Over the past few years, the prevalence of FeLV infec- Most dogs with lymphoma are middle-aged or older (6-12
tion in cats with lymphoma in the United States has been years of age); however, lymphoma can occur in dogs of any
decreasing, so we tend to see predominantly FeLV-negative age (even in puppies).
cats with lymphoma. Feline immunodeficiency virus (FIV)
infection increases the risk of developing lymphoma in cats; Clinical Features
cats infected with FIV are almost six times more likely to Four anatomic forms of presentation occur in dogs and cats
develop lymphoma than noninfected cats, whereas cats co- with lymphoma:
infected with FeLV and FIV are more than 75 times more
likely to develop lymphoma than noninfected cats (Shelton 1. Multicentric, characterized by generalized lymph-
et al., 1990). Louwerens et al. (2005) reported an increase in adenopathy; hepatic, splenic, or bone marrow involve-
the prevalence of feline lymphoma despite the decrease in ment; or a combination of these
the prevalence of FeLV infection; this increase was associated 2. Mediastinal, characterized by mediastinal lymph-
primarily with the gastrointestinal form, extranodal or atypi- adenopathy, with or without bone marrow infiltration
cal forms, and FeLV-negative mediastinal forms in young to 3. Alimentary, characterized by solitary, diffuse, or multifo-
middle-aged Siamese and oriental breeds. Helicobacter spp. cal gastrointestinal tract infiltration, with or without
may play a role in the development of gastric lymphoma intraabdominal lymphadenopathy
in cats (Bridgeford et al., 2008). Borrelia spp. infection has 4. Extranodal, affecting any organ or tissue (e.g., renal,
been linked to the development of non-Hodgkin lymphoma neural, ocular, cutaneous)
in people and in a horse (Ferreri et al., 2009); however, this
has not been described in dogs. A T-cell multicentric lym- The distribution of the different anatomic forms differs
phoma associated with infection with a novel Ehrlichia spp between cats and dogs. The multicentric form is the most
(Panola Mountain Ehrlichia) that responded to doxycycline common in dogs, accounting for more than 80% of all the
was recently reported (Qurollo et al., 2013). lymphomas in this species. In cats, the alimentary form is
In dogs, the etiology of lymphomas is considered multi- the most common, representing more than 70% of the cats
factorial because no single etiologic agent has been identi- with this neoplasm.
fied. However, a genetic component is evident in that the The clinical findings in dogs and cats with lymphoma are
neoplasm is highly prevalent in certain breeds and bloodlines related to the anatomic form of presentation. Patients with

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